I need advice please..

Hello. I'm new to glow and I'm mainly using it to help keep track of my period. I had two kids back to back by csection so when I had my son I've only had one period before I got pregnant again. Well I had my daughter she's seven months now and since I've had her my periods are off. I haven't had a period since August and I've taken tons of pregnancy tests and they all say negative. And before august I didn't have a period for three months. Is this normal or does that mean something isn't right? Please help me!