Singulair and slowing down

I have been taking Singulair for about a year and a half now, and my mild asthma is totally better. I have noticed a decrease in my shortness of breath, coughing, etc. and my allergy symptoms I struggled with for over 30 years are GONE. I also take Nasonex, so I can also attribute the improvement to that drug. But, I have had dramatic cycles of hair loss, which my hairdresser and doctor have attributed to "stress" even though I am not experiencing more stress than normal (except about the hair loss!) and the main thing for me is weight gain. I am a slim, petite 36 year old and I have gained at least 15 or 20 pounds since I started Singular. I have not decreased my activity level ( I am a waitress and walk about 5 miles each shift easily) or increased my food intake. My doctor and gyne keep telling me it's due to slowing metabolism, and implying that I'm slowing down in activity. I am not. I think it's the Singular, but I'm afraid of the allergy symptoms returning. Anyone else with significant weight gain?