But when i started measuring the bulb (3.5w) i found that only in 1 direction i found about 5M of resistance, from which i came to the conclusion that it is actually a DC-Bulb running on 110-120v
No such thing as a D.C. filament bulb. Not sure what you have. Do you have a link?
Also if a filament bulb did have 5M resistance in one direction and nothing in the other it would not light anyway.