You definitely need to go see your primary care doctor
about this problem right away. In addition to bruising, there are a few other medical problems that need to be ruled out.
First of all, your doctor can examine the purple areas and confirm that they are in fact bruises. If they are, then you will likely need a workup to determine why they are not healing. It is not common to have a bruise
last for 4 months without improvement. There are several different bleeding
disorders that could be associated with this trouble. Furthermore, rarely, persistent bruising may be a sign of a blood cancer, such as leukemia or lymphoma.
If these purple discolorations are not in fact bruises, as determined by your doctor, then they probably need to be biopsied. I would be concerned that a purple discoloration under the skin could be a melanoma, which is a very serious form of skin cancer that always needs to be ruled out in cases of persistent and suspicious discolorations.
Start by seeing your primary care doctor as soon as possible. They will help you figure out what is going on and what you need to do next to work this up!