Is that blood!?

When I started reading your answer I immediately thought of blood clot. I understand you have said you are going to see a doctor and I can't stress how important this is that you do it right away. A blood clot or DVT is treatable but only if caught right away. If this is what you have, if it travels to your brain, you would have a stroke or aneurysm and die. This has happened to young people. Since you noticed this symptoms 3 days ago, please go to the emergency ward. They can prescribe blood thinners for you that can dissolve the clot but if it detaches and travels to your brain it will be too late. Please get medical help to deal with this while you can..