I had a vag u/s at 4 or 5 weeks and there was no fetal pole. Went back at 8 weeks for another and everything was fine! Congrats on your pregnancy!!!
It's completely normal for no fetal pole to be seen at 4 weeks, some women don't even see it until 7-8 weeks. You're lucky you saw anything at all. I wouldn't worry at all, if you'd feel better ask your doctor to do another U/S when your 8-9 weeks! Congrats!