Serious Question About the Depo Shot

So I got the depo shot 5 days go and mannnn have I been Moody. Anyways, my question is, is their a chance that this shot could make me more fertile? I know I know, silly...I understand it's suppose to prevent pregnancy by injecting hormones into me & something about the thickening of discharge (I might have said that wrong /:) but before I got on the shot, I had irregular periods. It was like, every other month I got a period. I was curious to know if this shot would make it normal or am I just worrying too much. Also I read online that you can start having unprotected sex 7 days after the shot. Would I be safe if I waited 3 weeks? This is my first shot. Thanks to those who answer!