I've had bleeding in early pregnancy and the baby has been fine- I've also had it and lost a baby. The blood tests will be an indication of if everything is ok or not- I would also call back and request a sonogram, but it's possible, if you think you are only 4 weeks along, that they want to wait on that. There isn't much to see at 4 weeks.
Unfortunately, it's usually a waiting game with this sort of thing, get a blood test, then another a week or so later to see if your numbers are going up- waiting is so very hard, but it's hard to tell if everything is ok until the pregnancy progresses sometimes.
Let us know how you and baby are doing after you get your test results!
I had a mc at 6.5 weeks. You will know if something is wrong. There were lots of clots and blood was bright red. It started light one morning and got heavier throughout the day to the point of heavier than my normal period. I bled for almost 2 weeks. The fact that yours is stopping and starting is hopefully a good sign.
I spotted/bled from week 6 to 16 of my pregnancy. Red, brown, heavy, light, almost very single day. My twins are almost 5.
Hang in there! Drink 80oz's or more of water a day, or more. Keep your feet up as much as possible.
You are very early in your pregnancy, and an ultrasound wouldn't show much right now.
Hang in there and try to not worry.
Congrats on your pregnancy!!