Dull Cramping and really bad lower back pain

Hi ladies , so im 6/7dpo and ive been having cramps mostly on the left side( like a dull stretching feeling) and really bad lower left back pain. Last night i couldnt even bend over, today is not so bad but i still the cramping here and there. I have two kids ive never felt this before. Ive never felt implantation cramps before and i never get any type of cramps when AF comes around. I just want to know has any one felt this and had a bfp after? And is this type of cramps is considered implantation? Thank you