I have always had very painful periods, which have got worse as ive got older. Have often ended up on the floor in pain. Periods aren't heavy though and never have been.
I did once ask for it to be investigated, as I am pretty sure I have endo, but my gp refused to refer me unless I tried having a coil first 
Anyhow, the past few months ive been getting pain in my back, either side of my spine, low down, and moving around to the sides. It's a dull ache, that feels like my insides are aching, not my back, if that makes sense. It makes me feel really tired, and at the same time I also feel really full, and like I have eaten too much.
This month the pain was really bad, and came about half way through my cycle, and lasted for a week.
So, fast forward to now, and my period is late. Back pain is there ocasionally but not much, but i do still feel full alot of the time, and tired.
I know I should just go to the docs, and I will when i get 5 minutes where I am not sorting out someone elses ill health, but does this sound like a cyst ?? Google is saying yes, but I know it's bad to google lol