How can you tell if a cut is infected? I'm a 15 year old girl and yes, I cut myself. Anyways, a few of the cuts on the upper part of my thigh are taking a lot longer to heal than most of the other cuts have. They keep opening up and bleeding and sometimes

Pain, red, discharge. Keep them clean with peroxide and they should heal if superficial. It is time for you to find that therapist and talk. It is amazing what a skilled person using guided imagery can do to get to the root of your pain. If you want to feel something normal again after what you have been through, you must do the work. The cutting just provides a temporary distraction. .
Infection . Infection would be more red, painful, with yellow and green discharge. Clear fluid is more due to how deep you cut yourself. Put some antibiotic ointment on there. And make sure you go talk with someone for cutting. Sounds like you need to be on medication for potentially depression.
Infection Signs. Signs of infection are redness, swelling, pain, increased warmth, and purulent drainage (pus). Delayed wound healing can be the result of an infection as well, but it could be due to multiple other reasons. You should have these wounds looked at by a medical professional as soon as possible.