Birth Control question

I started my birth control about 2 months ago. I am 32 and this is the first time I ever use it. Despite the fact that it gives me really light periods, and no cramps, it makes me gain weight. Is that normal? I don't want to change it because it doesn't make me moody and I started working out more so I can keep at 135lbs. But I am worried I will get really overweight in the long run. Another issue I have with it is that a week and a half after my period ended I spotted for 3 days. Is that normal? I am so new to this...everything freaks me out. Any insight u ladies might have I would truly appreciate it. Thank you in advance