Severe cramps- anyone??

Hi, I'll be 6 weeks pregnant tomorrow. On Monday I had severe cramps for around 7 hours. They came in waves every couple of minutes and lasted for about 10 seconds. The waves of pain got stronger and stronger until they stopped and I managed to get to sleep. I was in absolute agony.
I've had no bleeding since and I still have all the usual signs that I'm pregnant- sore boobs, frequent urination and very tired.
I called the midwife but she said there's nothing that could be done as the baby is still too small to show up on a scan. She said not to worry and a lot of people have cramps....
I understand that pregnancy causes cramps but these were waves of agony that lasted for hours. I guess I'm hoping someone else may have experienced similar and had a successful pregnancy or is this a miscarriage which I really feel it is.
Help please??