I take 500mg metformin daily for 2 weeks now and feel fine.what are the chances of lactic acidosis?does it happen at any time or during the beginning?

No, if healthy: If you're healthy, kidney function is normal, not in heart failure, not dehydrated; then the risk of lactic acidosis is very low. The association of metformin and lactic acidosis is actually somewhat controversial, it was seen in a different drug of the same class that has since been discontinued, but physicians and pharmacists still warn about it just in case.