Pregnant or an Infection? (Or nothing)

I am 13, and I have been frequently masturbating for about 5 months. Before that, I didn't masturbate for about 3 months, but before that a frequently did for about 2 months. In that sense, I am sexually active. But not with a male (or female for that matter). 

I have had depression since about April 2015, and anxiety since about June 2015, and insomnia off an on for years. So I might just be very stressed about things. 

My first period started about June 2015, and was on a frequent cycle until August, in which it lasted a whole month. My next period was around the end of September, and I haven't had one since. I have had heavy discharge since I was about 11 years old. Around July 2015 it started getting really heavy and I thought that it was my period a few times. It has had a slight odour (kind of sour, I thought this was normal though). It has been too heavy to the point where I have needed to wear panty liners and it has soaked through the liners. 

I get pms symptoms but my period never comes, like cramps, discharge, headache, nausea.

I use both tampons and pads if that helps. 

I have been noticing my belly getting a little bigger, but I think it's just a little fat and not a baby. 

I know there isn't much possibility of getting pregnant without having sex, but I'm pretty worried about it. 

Please tell me what's wrong, or if this is completely normal.