Metformin new user

Hi all, i am new to type 2.My HbA1c is aprox 53mmols which the doctors says i,m borderline.The diabetes clinic has put me on Metformin 500mgs x 1 per day.I,ve been on this for 5 days but keep getting nasty stomach upsets in the morning and makes you feel weak.Does it wear off or should i come off them Any thoughts.I,m 68 with a quad bypass and mech aortic valve so already on different tablets.But am fairly fit.