Sonogram Issues

So according to my period i would be 5 weeks today. Went to the Dr today and the sonogram showed no sac. He saw something that looked like what he thought was a very tiny one. 
I have PCOS so im very irregular. So he seemed like everything was fine because he said i may not be 5 weeks i may be much earlier. He said my uturan lining was very thick and was a def sign that i was pregnant. He scheduled me for another sonogram nect week. Has this happened to anyone else? Worried ?