I think your intuition that this is something you need to see your doctor
about is exactly correct. Any major change in your menstrual cycle or any new bleeding
pattern should definitely be investigated to see what is going on. Any primary care doctor
should be able to help you out, so I would look for one of those as soon as possible!
A couple thoughts do occur to me. First, I wonder if you are using birth control pills. If so, break through bleeding (which is bleeding that occurs in the middle of the cycle) is pretty common, and it can start to happen even if you have previously been taking the pills for a while. Sometimes this requires switching to a different birth control method.
Second, are you taking any seizure medications? Sometimes, certain seizure medications can produce a serious complication in which they suppress the bone marrow. When this occurs, the levels of platelets in the blood drops, and easy bleeding can result. This is a really serious problem that needs to be diagnosed and managed immediately.
Next, you will need complete pelvic examination, looking for any evidence of fibroids, infections, or ulcers on the cervix, all of which could cause persistent bleeding.
Find a doctor as soon as possible so that you can get this taken care of. If you can't find a doctor quickly, go to an emergency room for evaluation, at least to rule out the possibility of a problem with your platelet levels.