Bleeding during first trimester?

I am almost 10 weeks pregnant and this morning when I went to the bathroom I had bright pink blook in the toilet paper when I wiped and a few drops on the toilet. I have been extrememly constipated and I was straining a lot (sorry TMI) I immediatly called my doctors office but they don't open until 1pm today. I have been checking every so often since this morning and the bleeding has stopped. I don't have any other symptoms at all, no cramping, no backpain...nothing. I have noticed tought that my are not as sore as they used to but I can't remember if that eventually goes away as you become more pregnant or not. Has this ever happened to anyone??? Could it have been caused by the straining when going to the bathroom???