What exactly does contractions feel like?

I am two days past due and I am wondering if I am reading my contractions correctly. My Obgyn told me that my contractions should last a minute and once they are less than five minutes a part, I should head to the hospital, however I have been recording my contractions at 7-8 minutes a part for three days now and nothing has changed and I am wondering if what I am feeling are even contractions. 
To me they feel like menstural cramps that spreads from my uterus towards my belly. And the pressure gets tighter and tighter until the tension finally releases. Is this right, Is this what contractions are suppose to feel like?