llo there, thanks for your query. I understand how it must feel when you gain so much weight in a short span. Let see what s happening. I see when you say your diet pattern has not changed. In that case do check, Step 1. If you are up late in the night and sleep deprived and stressed as all these cause increased appetite and you are more likely to consume high calorie foods. Do relax and include lots of fruits and veggies in your diet. Are you exercising regularly to burn the amount of calories you consume? A reverse equation will cause you gain weight very quickly. Do get involved in a regular exercise program. Has your thyroid hormones working just fine? Get your thyroid profile ( serum TSH and free T4) done to see if that is causing you gain weight. Are you on any drugs? ( steroids, anti depressants, antipsychotics, birth control pills) Have you noticed excess fat around neck and weight? ( it can be a sign of Cushing disease, a tumour that secretes excess cortisol) Do you have polycystic ovaries? Step 2. Its hard to talk about your bloating, pelvic and back pain as i cannot understand the nature of the cysts in your ovary. Do talk to your doctor regarding the ovarian cysts and what needs to be done about it as treatment depends on the nature of the cysts. Step 3. Your symptoms can just be related to severe pre menstrual syndrome. You can try oral contraceptives which has spironolactone to reduce fluid and water retention and bloating. If your ovarian cysts are simple, it may aid in its disappearance although there is no evidence for it. Restricting salt and water towards the end of your cycle may help a bit. Hope this helps. Good luck!