Take it as a compliment
If people are saying that, they obviously see something that you cannot. People have been saying that to me recently, even though according to the house scales I'm putting it on despite all the exercise and healthy eating I've been doing
Also remember that weight can vary depending on the time of day. They say it's better to weigh yourself first thing in the morning. Personally, I would say to the Psychiatrist about it, especially when there's medication involved