My fasting bs is avg 90 since 2 months, i started with 1000mg/d metformin when my bs was 300+(3 mnth ago). do i always have to take same dose forevr?

Maybe (not) . . .: It all depends upon whether you're able to make enough lifestyle changes to resolve the issues & risk factors that led to diabetes. In other words, for most people, it's a question of eating right & exercising enough to lose weight. Not to be rude but most people aren't disciplined enough to do so. However, there are some who are able to lose tremendous weight via lifestyle & come off medications.

Depends: It depends on your degree of control and what else you have been doing to lower your blood sugar. See your doc to get your a1 c recheck. You might have higher numbers after meals which you are not checking. It's not all about fasting.