Happiest, firstly you need to figure out why you are gaining or retaining the weight. That would mean you need a full physical work-up with labs. Go to a good endocrinologist and not just an internist. A good doctor will check everything out to make sure all systems are working ok. Then he will discuss with your other doctors if any medication can be changed to those that are not weight gainers.
This is NOT something someone else can recommend for you. What works for one may not work for someone else. Everyone has to deal with their own metabolism and genes. My doc figured out that my metabolism was basically not working and that there was something else off. I needed a certain medication to balance things out for me and I lost weight by not only taking the meds he gave me but also by following the rules he gave me. I get regular blood work so he makes sure everything is ok and I am doing the right thing.