Getting a little scared

So yesterday my husband and I went for a walk around the lake we are at its was just over three miles and I felt perfectly fine. Then in the afternoon I noticed some brown marks in my underwear. When I wiped it was still a brown red color so I wasn't worried but I laid down and put my feet up. Then this morning it was about the same but it has gotten more pink as the day has gone on. I called the doctor and I go in at 3 this afternoon for an ultrasound and blood work. I'm really nervous that this is a sign of misscariage since my older sister had 3 and my mom had one. Any advice?