How do I know if I am breakthrough bleeding or implantation bleeding if I think I am pregnant?

My period was late. I was on the patch. The first week of the last cycle I put it on late and I ume that is when I became pregnant. The last day of the week that my period was due, I went to work and used the restroom. There was a little of blood on my underwear. I have lost one child and I don't want to lose another. How do I know if this is implantation bleeding or breakthrough bleeding and how can you tell the difference?