My very first symptoms where cramps, and I thought I was just expecting my period didnt give it another thought. Took a pregnancy test a few days later and I was pregnant! Still cramping at week 13! Sometimes the cramps even wake me up at night! Your uterus is going from the size of a pair to the size of a grapefruit really quickly and you would be lucky not to feel those changes =) It sounds like the normal stretching! If you are really concerned I recommend getting into a doctor! Good luck =)