Just put on metformin since monday, i'm having extremely bad sciatic pain and pain in hip girdles. why is this happening?

Coincidence? Strain?: Or side effect? Check out http://www.Drugs.Com/sfx/metformin-side-effects.Html for list of some side effects associated w/metformin. Then go see your doc to determine if coincidental or side effect. Metformin is a great drug for diabetes so you need to determine how bad pain bothers you. You're the judge. Of course, don't forget to improve your nutrition & exercise regularly. Then might not need.

Depends: Depends on the location of the "hip." the term "hip" is often not specifically localizing, even for physicians. If pain in in the groin, actual hip joint may be involved. If pain is on the side, it may be bursitis. If pain is in the butt, other possibilities. This would have to be localized and then specific treatment of bursal injection, identification and assurance of no fx.