why am I busting my @ss to gain weight?

sometimes weight loss just takes time, Relax you'lll get there eventually. And gaining 1lbs is nothing!!!

You are not eating enough on the days that you are going to the gym..... not eating exercise calories might work for people that has lots of weight to lose, but when you only have 10lbs to lose you need to eat more of your exercise calories...

Time and time the people that has been on here for a while and that has figured it out the hard way will tell you that the moment they started eating more the weight started coming off....

Have a read of this to understand the concept of eating your exercise calories

http://www.myfitnesspal.com/topics/show/61706-guide-to-calorie-deficits

P.S Make sure you are eating enough!!!! Otherwise, your body will NOT burn the food you're eating. Instead, it will hold onto everything that it can.

It is harder when you don't have much to lose in the first place.

First off, don't worry too much about 500g fluctuations - I know it's frustrating; my weight fluctuates by up to a couple of kg from day to day. I use daily weighing to work out overall trends, but that's not for everyone.

Secondly, and I know it's an ages-old MFP debate, but I don't think you're eating enough on your exercise days. YMMV, but you might want to try eating back some of your exercise calories, particularly in the form of protein. When I plateaued, I only got past it when I increased my calorie consumption on both active and rest days, and switched my eating pattern around.

Also, you say you're doing arm weights - do you mean bicep curls and the like? If so, I'd be inclined to switch to composite lifts (squats, bench presses and deadlifts being the heart of such a routine). Lifts that target smaller specific muscle groups are really most useful for tweaking existing muscular development. And remember to EAT after lifting, otherwise there won't be anything to help grow the muscle that'll increase your BMR that'll burn more calories on a daily basis.

I'd also recommend working out with an HRM - exercise machines and MFP estimates can both be seriously off. For example, although my strength work burns far more than the MFP estimate, I don't get anywhere near the calorie burn I used to from cycling because my body has become more efficient at it. The same applies to most forms of cardio. For similar reasons, it's worth changing up your routine and doing different types of exercise that you're less used to.

Um. Okay. Long ramble there. Hope it's of some use.

Usual disclaimer: I have no qualifications and speak only from personal experience. Take all advice from strangers on the internet - including me - with a pinch of salt.

I am having same problem. I to was not eating enough calories back.
Now gaining muscle can also mean getting heavier for a while. It will all be ok in the end.

I took a quick peak at your diary. In the past few days you logged no water. Plus, you have been eating processed meats (genoa salami and turkey breast). These are loaded with sodium which makes you retain water weight. Since you're not drinking water, your body may be holding on to it. Try reducing sodium intake and increasing water intake. See if that helps.

Wow! So many great,helpful replies! Thank you all! You just helped me too!

Food choices are pretty good and so is the number breakdown per meal. I don't see how much water you drink in a day and that water helps a ton!! I drink 1 gal a day. Plus eating back some of your work out calories helps with the body removing unwanted pounds. I know that is seems weird but it does!! I hit my first plateau and started eating back 1/2 of my workout calories ans now I am back to losing again.

So, I would say that eating back some workout calories and drinking 8+ glasses of water might help you.

Plus some of that weight gain could be due to muscle mass increase.

I absolutely agree with everyone who said to eat more. I don't think you can really gain muscle mass on so few calories, but your body does retain fluid in your muscles with heavy exercise, especially if you're new to it. Add some high sodium foods, and you've easily got a couple pounds extra in water.

Heck, I had pizza and boneless wings and some vodka last night, and I'm "up" five pounds from where I was last week. But I know, realistically, that I didn't eat enough to gain weight, and it'll be gone in a few days. Because to gain 5#, I would have had to have had 17,500 calories above what it takes to maintain my weight, and I sure as hell didn't do that!

If I were you, I'd set my goals to lose a half pound a week, manually increase the protein (some days you get a lot, which is good, some days hardly any), eat the exercise calories, and eat a little bit more at each meal. I personally try to get over 100g of protein a day. I don't fuss about carbs or fat, but I feel better and perform better when I get plenty of protein.

Also, realistically look at something that weighs one pound. A 16oz glass of water, for instance. That one pound, spread out over your entire body, is NOT worth feeling bad about!