WHY am I gaining weight??

The healthiness of your meals won't make a difference if you're not getting enough calories, though you look like you have a great diet! On days where you run, do you eat your exercise calories? 23 miles a week would burn a lot of calories...and if you're not eating some or most of those back, then your deficit is too large..which would cause your weight loss to stall. I'm guessing you burn more than 400 calories during a 7 mile run, right? So even when you're eating 1600 calories, you're still not netting enough (you don't want to be lower than 1200 NET at the end of the day). If you try to add more calories into your day (extra protein shake, nuts, good fats, more snacks..) then you'll see improvements. At this point any strength training you do isn't really helping you because there's not enough fuel to go around in your body, so your muscles cannot build. If you eat more, you will notice improvements with your energy, muscle mass, and weight loss. It's just one more thing you can try if you find this plateau to be a persistent problem.

Totally agree with this and was going to post about upping calories with all the exercise OP is doing. Thank you for saying it so well and saving me the trouble. Just copying it to emphasize how important this is.

Thanks for posting this question and the answers. I was wondering the same thing because yesterday I had an intense workout that included about 7 hours of intense activity. I was wondering why this morning I gained 1.5 lbs, when yesterday I wasn't able to eat my calorie deficit and had almost a 2000+ deficit for the day. I had a huge meal after my workout and was so thirsty when I got done, I downed tons of liquids, much more than I usually drink. But I literally couldn't force myself to eat the rest of my calorie deficit.

The water retention due to muscle repair makes sense to me. I also have one of those body fat scales but I don't think it's that accurate to be honest. For the longest time, it has listed my water weight as 51%...which seems strangely low. I could literally feel my muscles in that sort of restless pain you get after a hard day's work.

I know a lot of people say not to weigh yourself everyday, but I don't think there's anything to wrong with it. It's actually been more useful for me to weigh myself everyday and see the fluctuations for myself from day to day but see overall how my eating/workout changes have made a difference over time. As long as you don't freak out and feel hopeless because it's not showing you what you want, and as long as you take the number with a grain of salt, knowing that it's not necessarily the perfect or only indication of your progress, it's ok.