Period after 5 years of not having one!

Okay ladies. I was on the depo shot for 5 years for irregular periods. Well I never had a period the whole 4 years but the 5 year I started having major problems with the bleeding and cramps and female problems. Well I got the nexplanon implant in November of 2015. I just now started my "period " on this past Sunday. Well at first it was very dark brown and then yesterday it went to a normal blood color. I've been very very emotional and can't control it. My cramps are starting to get unbearable! At first I bleed heavily. But now it's like a light/spotting flow. I'm not sure if this means I'll start having a period again or what's going on. I am very sexually active. Any ideas of what's going on with my body?