Married- Periods late by 2 days. Tomw?

Hi, My periods are usually 31 days cycle and I last got my periods on 8th March. When I have been too much stressed out I had been max late for 5 ( happened once). But this time it's only 2 days due and I am concerned as I am feeling some weird symptoms. I am feeling extremely tired , I have lower back pain since 3 days, I am feeling lil dizzy , frequent urination too( I am drinking 2lts of water), experiencing slight stomach cramps today.I am also having slight fever now -and- then since yesterday. Are these signs of pregnancy or just flu or is it just normal to have these symptoms before periods? Since last two months I have had perfect 31 days cycle and even if my periods are sometimes 1 or 2 days late I have never had these terrible back pains and tiredness. Can you suggest if I should wait or see a doc by tomw? Thanks in advance.