long term cramping.. pregnancy?? HELP PLEASE

In pregnancy is it likely to have period like cramping all day everyday from the moment you conceived till like now around 21 weeks. 
I don't think I'm pregnant because I have had negative tests and periods still. But I just want to get pregnancy out of my head because I can't stop thinking about 'what if?'
So if I was to be pregnant like wouldn't cramping be not a good sign ? 
The pain feels exactly like period pain and it aches in my groin and lower back and radiates down my thighs and even my bum cheeks. 
I have literally had the pain for 21 weeks now, I have been to the doctors they said I'm not pregnant because I have had all negative HTPS and periods. 
I really don't want to be pregnant- as to why I'm stressing about it. 
I just don't understand why I have period pain everyday. It has just woken me up from my sleep and now I can't get back to sleep because of the ache.