birth control options?

So I've been in a serious relationship for about a month now but I absolutely do not want kids at any point in the near future. Like.....it can't happen. Up until now we've been using condoms and withdrawal but I want to be positive that there's not gonna be an accidental pregnancy. So my question is, what is the simplest form of birth control? Everything I've ever heard about bc has been terrifying. I just want something that will prevent pregnancy, but with as few side effects as possible. I'm also on sertraline (an anti-depressant) and I'm a little concerned about the interactions it might have with whatever form of birth control I choose. 
Basically, I just want something that won't make me break out like crazy or gain tons of weight because I just spent a year trying my best to LOSE weight. Which is a lot to ask, I know, there are always gonna be side effects to birth control, but is there anything out there that will cause me the least pain while still ensuring that I don't accidentally get a bun in the oven? Just something that's simple, not complicated, and does its job. Something not completely scary.