Bloating, Indigestion, Irregular period, Pain?

From mid December something has been wrong. I know my body well. I was scheduled to get my period on Jan. 18th. Got a blood test done to rule out pregnancy about 8 days after that scheduled period was skipped and it came back negative. I am experiencing extreme pain occasionally on my left lower backside (kidneys?), fullness, bloating, some constipation although I still move my bowels each day each day, rapid weight gain (12 lbs in 1.5 months), insomnia and chronic indigestion that I cannot get rid of. Also, last time I had I experienced painful cramps about 2 hours afterwards. I have a dull ache in my abdomen frequently. What should I schedule? Blood tests? A gyno exam? I am embarred about the weight gain and can't understand it as I haven't changed my lifestyle or eating habits. Something is wrong.