Contractions

Does anyone have a better way to describe contractions other than "very similar to period cramps"? This is the only comparison doc has given me.... FTM, and I've been lucky enough to miss out on period cramps my whole life so not sure what exactly to look for, and have been miserable the past week with back pain and as of last night pain similar to a "belly ache". Little Man is constantly on the move, so not too concerned. More curious as to what to be looking for! 38 weeks