Likewise, I've never noticed any appetite or weight issues from the antihistamines. I took a number of different kinds over the years. Starting around 2000, I mostly took cetirizine (brand name "Reactine") because most others had a conflict with the antidepressants.

I'm in my late 40s and have had to take antihistamines during the growing season almost all my life. Often I can get away with as little as once a week until ragweed season. On a really good year, I can hold off entirely until then. Some years, the hayfever is bad enough to require the prescription nasal sprays in addition to daily pills. Sadly, no other treatments or home remedies have ever really worked for me.

Actually, I've never personally noticed any side effects of any type from an antihistamine, not even fatigue. I guess I'm lucky in that.