What Could Be Causing My Abdominal Swelling, Weight Gain, And Alternating Diarrhea And Constipation?

Hello, I hope you are well. I have a question about my stomach. I have recently in the last 8 months-1 year and I have gained a weight on my stomach as well as have diarrhoea and then constipation and sharp pains in my stomach. I have been told I have a low thyroid but then my blood results came back normal after medication. The main thing I’m concerned about is how swollen I am and how I have gained weight. Would you please be able to help at all? Thank you so much