<s>[INST] In the last two months I been gaining weight, mostly in my mid-section. Right after my periods I've been getting real sick. When went to the doctor she said I had the flu. my body was aching, headaches.But, I've been having lower mid-abdomen pain as well. Even cramping along with nausea  and it always start a few days after my period ends.As well as my period been irregular. I'm 24 and 5'7. [/INST] Irregular periods needs evaluation. Weight gain could be due to irregular periods. To know the cause I would suggest you to do a thyroid function test, serum prolactin . also do a ultrasound abdomen to rule out gynaecological causes of irregular periods. </s>