HELP!! Agrivating plateau making me want to quit

The scale is just a number. How do you look/feel?

I had a big cheat meal on Sat and added a good 5 pounds to the scale and it stayed stuck there for 3 full days. I paid little attention to it as i know it isn't reflected in the mirror. It will go down eventually. keep on plugging along!!

It's only been 2 1/2 weeks. The fact that you have very little to lose makes it much more difficult because a few meals of over-estimating can keep you at the same weight.
Also, I don't think you can alter a metabolism in 3 days. That's something that takes a bit of time either via building/losing muscle or increasing cardiac output, etc. That takes about 6 weeks minimum. Your body's metabolism is not so easily swayed by three days of over-eating.
If you're going nuts and frustrated maybe it's time to look into something different? Are you eating the same food all the time? Maybe there's different recipes, different macros you can try to change it up that will still keep you in caloric range?
If you're just running then maybe you want to change that up a bit? Do you do sprints during your long runs or run up hills? Do you do anything else besides Jillian Michael's videos? Maybe join a class or find different youtube workout videos to change it up and challenge your body more? With that distance you're running as well you may be retaining more water because the repair on damaged muscles from 12 miles is extensive and will take some time to recover, not to mention the repair on the joints as well.

I think you're doing a great job but there's going to be plateaus with any weight loss, particularly as you have less and less to lose. It's important to have other goals as well - measurements you can make to see changes? workout goals, etc and not be as pre-occupied with the number on the scale.
Also, "starvation mode" is not a thing. But if you're eating less than you burn everyday and you've tried to make other changes to no avail then maybe a check up with the doctor for blood work to make sure there's no hormonal issues, or medications you're taking that may be slowing down your progress.

P.S. A few years ago when I was at my thinnest I was running extensively as you were and I was lifting a lot too. My weight hit 145 pounds on the scale, and stayed there for months. BUT I went down 3 pant sizes. I think if you're doing as much as you say you are doing then there should be other noticeable differences in your body that you can focus on besides that number on the scale. I was annoyed too that I was running 5-6 miles 5 days a week and lifting but that stupid number didn't move. But since I thinned out so much and I fell down to a size 6 I was able to not become so number obsessed on the scale

Running messes things up because you will retain a lot of water working those muscles.

I agree though, you're probably eating more than you think.

If the running is new you are probably retaining water/gylcogen stores from the new exercise.

This can take up to 6 weeks to go away.

Increasing calories does not increase metabolism...

YOu mention you weigh your food but do you log accurately and consistently...using correct entries and logging everything?

I've had experience with true plateaus myself. True plateaus are uncommon, and most who think they are in a plateau are not in a true plateau because they are unknowingly eating at maintenance.

The part that makes the least sense is that, during a true plateau, one should have weight fluctuations. It may go up and down 2-3 lbs. (sometimes even more) from day to day and even hour to hour. I know you mentioned you trust the scale, but no fluctuations is highly unusual. See if you can use another scale - at the gym, at a friend's place, etc. If possible, bring your scale so you can weigh on yours and then on the other right away... see how far apart they are, and repeat a few times to see if the gap is consistent.

Let's say you are in a plateau - in a true plateau, a person does not lose regardless of how little they eat and does not gain regardless of how much they eat. This is true up until the end of the plateau. Try raising calorie intake by 1K calories per day (more if you are able to eat that much) for 6 weeks. If you are in a true plateau, then you will not gain. If you notice you start gaining, then you have proven that you are not in a true plateau... in that case, reduce calories again.

If, after 6 weeks of high calorie intake, you find that you ARE in a true plateau (i.e. you haven't gained anything), then you should continue what you are doing because there will be a "whoosh" eventually. It may take 6 months or longer, but true plateaus eventually end with the result that most would see more quickly and regularly. Try not to get discouraged. Keep doing what you need to do and trust it will make a difference. I know it is tough - I've been there myself, and nearly quit during long plateaus.

Do you track your weight daily? I started using happy scale about 3 months ago and now I am not scared if my weight changes constantly. For the last couple weeks it was TOM and then last week I was weighing 2 lbs more then before (about 132 at 5"3), I kinda worried but I still recognized my clothes are fitting way looser and I can tell in my stomach. I started using 6 lbs in extra weight when doing strength training so I took it as maybe its water weight from this or I've been sick for the past couple of weeks it could be many things. Now this week I'm down to 129ish and I'm thinking I worried for nothing. Just don't give up I know its frustrating but I had the same thing happen and all of a sudden I was down 3 lbs! So keep going!

Also maybe you're 1 lb a week weight loss is too aggressive, I started at 138 and did .5 lb a week and found it much easier and I've been losing at that rate since the end of Jan. Remember the longer it takes to come off the longer it will stay off.

Step away from the scales. You are fit as a whistle running half marathons and everything. So what is your goal?? Being fit and healthy, or seeing a number on the scale??
Don't let the scale-number bring you down, as that will have an impact on your routine as well.