It is not uncommon to have persistent swelling after eyelid surgery. It is normal for the lids to swell intermittently for many months when you are retaining fluid, when you eat salty foods, when you are sleep deprived, etc. If your lids are red and itchy as well as swollen that may signify allergic reaction either to seasonal allergies or something you are applying to your eyelids (soaps, cleansers, makeup, latisse, etc.). You should let your doctor examine you and recommend treatment options.
You mentioned that your eyelids are swollen after 4 months and I am assuming that you mean 4 months after surgery. It can sometimes take 6 or more months for all of the healing to occur after eyelid surgery so it is possible that there could be some degree of swelling after 4 months. I would not say this is normal but it is possible. Swelling should be gradually improving however, so if you feel the swelling is getting worse or is more than mild, you should contact your surgeon to be evaluated.