Metformin Side Effects- HELP!

Caitlin
I just restarted Metformin 500mg 3 times a day. My orginal prescription was expired so I had to restart. I'm taking it once a day for week, then slowly building up to 3. 
The stomach pains and constant bathroom trips for number two are KILLING me and it's been a day. I been sipping Coke for the constant upset stomach but I want to LOSE the weight with this medication like I have in the past, but I need help kicking the side effects. Any suggestions?