Weird Period, Hormonal Imbalance, Or Decidual Bleeding? HELP!

Not sure if this Is in the right section I'm new here. 

Hi, This is long i know amd im sorry but im concerned and I need help. I hope this makes sense and sorry for the tmi! 

I was wondering if anyone has experienced decidual bleeding? I'm kind of confused. For 2 months my 'period' hasn't been the same..back in January I had unprotected sex 2 days before my period Jan. 21st was the starting day. I got my period but it only lasted 4 days and it normally lasts 6-7. My periods are pretty regular and never short. It was kind of lighter than usual the first day but not too light maybe medium flow like with little clots then the next day (day 2), it was light and kind of brown, day 3, it turned fully brown, day 4, brown spotting. There was nothing after. So I signatured it off as a weird period. 

A week or two after that, i had twinges of pain that felt like pulling and dull stabbing pains, maybe ovulation pain? 

In February, I was experiencing period like cramps a few days before my expected period and thought I was bleeding. So i went to check and there was nothing but watery discharge.

I ending up being a day late before i got my 'period' (got it on feb. 19), it was like the one in january but a tiny bit heavier and had some clots not a lot like normally. The 2nd day it turned dark brown and the 3rd day it was just scanty after that no period..

I'm not sure if this is a homornal inbalance or if something's wrong? My period has been pretty regular until that day my partner did his business in that place (sorry for the tmi). I kind of doubt I'm pregnant. But we did have unprotected sex during my period in January, as well on day 1. 

As far for pregnancy symptoms I'm only having fatigue, back pain, headaches here and there, and acid reflux. I'm not sure if I should buy a test to ease my mind, as I don't want to waste money if it's unnecessary. I'm also aware I ovulate more then once a month so I'm not sure when I ovulated. 😳

Have you or anyone you know experienced this? Your input would be much appreciated! Thanks in advance! 

Also we aren't necessarily trying for a baby but we also aren't preventing it..but a child is a blessing and it would be welcomed.