Spotting at eight weeks!

I'm trying not to panic but this morning after I went to the bathroom I  saw that there was brown blood on the tp. I'm also constipated and straining to go this morning. Called my doc and they said to monitor it and call if bleeding continues or turns red. They said the fact that I've been straining to go could very well be the reason for the blood. Still,I'm nervous. I haven't seen a trace of blood since my last period so this is scary to me. Next ultrasound is scheduled for next Friday. I hope it's nothing!!