I second Kelly's comments. And even if you didn't have transvaginal ultrasound, that cervix is so easily irritated right now. If you had sex it could happen along with a host of other reasons. I spotted and bled throughout my entire pregnancy. Scary, but he was fine. It is super common and doesn't necessarily mean anything is wrong. Give your Dr. a call on monday if it continues, but honestly, you have a strong heartbeat so I would bet all is just fine!!
You asked about how those of us with multiple miscarriages keep going. I have had 6 in total now. Pregnancy is a scary idea for me to be sure, but there is no other way to get to my goal. So I just take it one step at a time. I also have a great support system, both in real life and here...and I do use it. I lean on others when I don't feel strong enough to take care of myself. Not sure that made sense, but it's the best way I can think of to describe it. Take care, and remember...every day you are pregnant is a victory!! Celebrate that heartbeat..it's a huge milestone.
NO, don't get upset. I'm sure you had a vaginal u/s right? Your cervix is very sensitive and was probably irritated and bled a little OR it was left over blood just coming out. You just saw a healthy strong hb! Try to relax and monitor yourself, Im sure all is well.