Has anyone ever experianced this before?

Hi! So let me strat from the beginning, In febuary I had gotten my normal period on the 3rd, and then on the 20th I had gotten another period which to me seemed normal maybe just a couple days shoter. I track my period and was due for my period on March 6th, I did take a pregnany test on Wenesday and agian thursday morning, but both came out negative. I have also been experiancing some cramping which is right around my uterus, I was thinking that I was gy and constipated but I havnt been having any problems using the restroom, sorry if too much info. My question is could of gotten my period twice last month and may not get it this month (i never had my period twice a month before). Also, I have been off the shot for about 2 or 3 months now and with having two children we barley have and when we do we do uwe the pull out method ( which i know is not 100%) I did post this question on friday late night but did not get any helpful information, if you could give me any insight on your experiances that would be great! Also I never experianced this with my other two children, and should I just wait a couple weeks and restest? Thank you in advance.