Yes, you need a work-up to determine if any medical issues have caused you weight gain. If you are healthy, now is a great time to deal with your diet which is 95%+ of the cause of weight gain.
You should have your hormones evaluated or see a nutritionist/internist to determine what is best. The weight gain shouldn't be from the surgery its own. Best, Dr. Emer.
Rapid weight gain as you have been experiencing should be evaluated by an experienced physician. Definitely you should see someone.
Certainly you would want to check first with your primary care physician and see if there is anything metabolically that could be causing your weight gain. There is nothing about your surgical procedure that could be causing such a significant change in weight. Your primary care doctor may want you to see an endocrinologist of other specialist to investigate further.
An evaluation by your doctor will help.You need a history and physical exam and possibly some blood work. A referral to an endocrinologist is also possible. Best wishes.
Maybe you're pregnant. If not, go see your physician and have them run a few tests. Meanwhile, double check your diet and calorie intake. This has nothing to do with surgery.