Try not to stress - it is normal. There actually are quite a few threads on here regarding spotting, esp in the first trim section.
I had it as well - 5 weeks & 2 days. And then on and off for about 2 - 3 weeks. Implentation bleeding i think they also call it.
For me, my spotting was either brown, bright red, or watery red/brown. I had an u/s done, and then still had spotting, so had blood test to check hormone levels. and all was good. Dr will / should take it seriously, and get some further tests done, if he doesnt suggest it, then just ask for it to happen. The ones i had done where 2 days apart to check for differences.
If it is spotting, you will notice sometimes it is there, sometimes it is not. For me, initally, used to have abit of spotting if i hang out washing (stretching i assume) or vacumming, or even doing "it" with hubby. Apparently, skin is abit thinner or something in there, and can be brusied alot easier. Maybe abit of lube (sorry if TMI) if that is the case.
But, as i said in another post, i know exactly how it feels. i completely freaked out. had been trying for a while and i so didnt want anything to go wrong. And for me, i had no one at the time to get advice from, other then my mum and the dr. I wish i had of know about this forum them.