Well your description is a little vage but if you were bleeding for three hours then it is a big concern and what kind of a flow was it and what color.. All important questions.. You can still have a period at five weeks but it is rare and does not sound like that's what happened.. If the flow is very heavy seek medical attention right away if its spotting then call your OB doctor right away as these can be symptoms of something more serious...
I had the same bleeding at 4 weeks. But mine was with clots and cramps. It was concidered a threatened miscarriage. Anytime you have bright red bleeding you should seek medical attention. They will probably do a transvaginal ultrasound to make sure g sac is in the right place, and start to monitor your hcg levels to ensure they are increasing. Good luck!
Sounds like normal spotting. As long as it stopped I wouldn't worry. If you are worried about it, the dr can check your hcg levels.