Does Benadryl as a PRN cause weight gain?

I just talked to my doctor she said that it's ok for me to take Benadryl as a PRN but I'm worried because I heard it can cause weight gain. I don't want any weight gain and I was wondering if I only take it Monday Friday and EVERY OTHER Saturday if I'd still gain weight only taking 25MG at most. Sorry I didn't get a chance to ask her. But she did say I could take Gabapenin as a PRN that it could cause weight gain but if I take it once or twice a week I wouldn't gain weight. Mostly concerned about Benadryl Thanks.