I'm 5 weeks pregnant and my 9 months old fell back and his head hit my abdomen while i was laying on my back. should my unborn be ok? wouldn't i cramp/bleed if there was a problem?

The fetus at that stage is tiny and surrounded by protected layers of tissue/fluid that buffer any trauma. Without the signs you mention I would not consider the event as described a problem for your unborn.

What you described is not a cause for concern for the fetus. Do visit your doctor for regular antenatal care. Wish you good health and a healthy baby!