Rapid weight gain

So I was diagnosed with PCOS years ago and had been on birth control ever since. In the past two years I lost almost 20 pounds and developed a healthier lifestyle. I stopped talking birth control several months ago, just to see how my body was doing (if I would have regular cycles). I have been regular and keeping weight down by working out regularly, I feel good. This month, I am now 10 days late and have gained 11 pounds so far this month. At first I worried I was pregnant (tests negative, no other symptoms) because nothing has changed in my routine. I have a doctors appointment for next week, but I'm wondering if anyone has experienced such rapid weight gain? PCOS, thyroid? Drives me crazy to be putting in so much work and getting fluffier by the day.