Allergies/Antibiotics/Weight Gain

Can allergies inhibit (or help inhibit) weight gain?

I'm allergic to life (not as great an exaggeration as it may seem). Supposed to be on shots, and was for a few years, but the last couple of years I haven't been able to afford them. So...I pretty well in a constant state of reacting to something, to some degree.


What about antibiotics?

From the time I was 15 until 17 or 18 I took antibiotics once or twice a day every day (acne)...along with an almost completely fat-free diet for that same amount of time (yes, my dermatologist was seriously old school).

Would that contribute to problems down the road?

Could probiotics actually help relieve any adverse effects?

The reason I ask, is that I'm 28 now, and while I admit I haven't been super active the last year and a half and have been trying learn to how to handle stress in a healthier manner, I weigh less than i did when I graduated high school and even seem to have a lot of muscle atrophy and higher body fat than I would've thought I'd have at 5'11 & 150 lbs.
Of course...that's pretty well how I've looked all this time, even at my heaviest (185).

Just trying to pinpoint the problem(s) so I can figure out how to go about getting back on the road to being "healthy" again.

Any input? or suggested reading material?