When I was pregnant (10 yrs. ago). I had those symptoms along with bloated stomach and I couldn't completely empty my bladder. I went to the ER and found I had a very bad urinary tract infection. Never had one before so I had no idea of the symptoms. They inserted a cath. to help w/ the urine and gave me antibiotics. This cured me. Now there is a difference between menstral blood and blood in your urine. Which one are you having? If its blood in your urine then it may be a UTI but if it's from a menstral then you may just be having an early period. It does happen. Mine are usually regular but on a few occasions I have had them early or late with no explanation. This is my thoughts. Hope they help a little.
Have you ever had a UTI (urinary tract infection) before? It is very common for women to get these. They are very treatable with antibiotics. By your description it sounds like what is going on with you. There are even tests you can perchase at most stores/drugstores, wal-mart, walgreens,etc. to check your urine for any signs of an UTI. They are common, but don't ignore one if you have one becausethey can become more serious. I hope this helps you.
UTI, bladder-infection, renal-lesion, kidney-stone... all of those could be the culprit. As the above said though, all signs point to UTI.
A broad-spectrum antibiotic should do the trick, but a trip to your PCP or Gyno (or Urologist if you have one) might be worth it, especially if you haven't had a check up in a while.