Also, last week I was having some back pain as well, and I was feeling really bloated, and Constipated for like 4 days.
my periods usually last 7 days.. and last month it lasted 7 days and it comes the 7th of everymonth..
this month I lasted for like 3-4 days.. and I started on the 7th as well.. I had a light period, as usual, but my periods never last 3-4 days long!
It seems that it is urinary tract infection, at least it resembles. I was suffering from this condition two years ago and my symptoms were very similar to yours. I was urinating way to often and when my period came it was light, almost nothing, and it lasted only 3 days. And during urination I was feeling mild burning sensation. So you need to see your doctor about this and after examination he will tell you what you should do next. I was drinking antibiotics and I was advised to follow the instructions which doctor gave me.
This included drinking plenty of water every day and urination when the need arises and avoiding resisting the urge to urinate. He as well mentioned that I should try to urinate after sexual intercourse. After few days I have stopped feeling symptoms of the urinary tract infection. Hopefully this information helped you with your problem.