Urinary tract infection...?

I had back ache last night, I am about 2 days late for my period. I have been expecting to get it for the past several weeks. About 1 week and a half ago I started getting cramps and I was at work one tme when it happened and they thew me off a little bit and distracted me. They went away for a few days but they have been back the last couple and I swear my period is on, like it feels like I am actually on my period but Im not. Yesterday it felt like I had just started so I went to the toilet but there was alot of discharge instead. I have never had this before, or maybe just not notice, can you get lots of white discharge the day or the day before you start your perod? I never have but I just want to know if it is common? I had unprotected sex a little over 3 weeks ago, and a week ago had a tiny bit of spotting on tissue like hardly any just when I wiped but I also had a urinary tract infection that day so thought it was down to that, even though it wasnt from my urine. Any help is appreciated.