birth control pills

I really want to go on the pill because my period is still irregular and I just want to be extra safe, because I know im gonna be sexually active. I've heard that going on the pill causes weight gain sometimes and I'm really, really extremely sensitive and easily "triggered" when I gain weight (i eat a pretty healthy diet and eat everything in moderation, With no restrictions) and I'm just genuinely scared of gaining weight 

Does anyone have tips/ alternatives?