can anyone help?!

okay so, tonight i was having sex with my boyfriend. and it wasn't the first time at All, in fact it was out third time today. (probably tmi lol).. well anyways... he was just kinda doing his thing and for some reason out of nowhere i got really emotional and almost started crying?? nothing is wrong , i felt totally normal. our relationship is great. my life is mainly great... everything was great before we started doing it, but like i just wanted to cry? and for the past two days i've been having cramps in my back and abdomen. my period isn't supposed to start for another 10 days, which is too soon to be pmsing.. so what explains the random outburst of emotion and cramps? does anyone have any idea? please help !!