Zyrtec causing plateo?

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I was having good weight loss - a pound or two a week. Then I started getting the allergy shots for my sage and tumbleweed allergies. They told me I had to take Zyrtec to control the reactions when I have shots. (Which have been pretty small compared to reactions that I see some people have.)

But now I have stopped losing weight. I try to eat about 1200 - 1600 a day. I started exercising more. I eat home made stuff like vegetables, meats, eggs, some dairy, nuts and a few fruit, rice now and then. No processed stuff. But I am stuck at the same weight.

I will be getting my thyroid levels checked at my next appointment, but am wondering if anyone else has had this issue. According to Livestrong, some people do report gaining weight while on antihistamines. Anyone here have that reaction?