A little help here ladies!! Please

I have been having cramping for four days straight (through out the day), pms like cramping, no bleeding at all and had lower back pain for a day... AF isn't due for another 6 days. The cramping has stopped. I'm never late and I always have cramping a day before AF. So the cramping for four days worried me. Can anyone please explain what the cramping could be? Hoping for a baby!! Been TTC for 6 months now