PLEASE HELP Settling debt with collections for medical bills?

So I checked my credit karma, and my score went down 64 points because of 3 derogatory marks. I m only 20, and I got to school full time.. I only work PRN, so I come in as needed. I m looking for part-time employment, but I m really trying to focus on school. I called the debt collector, and paid half of my balance (removing two accounts). She told me the next cycle the bills will be removed off my account, and we set up a payment plan for $20/month for the last account. All I owe left Is $198. because I paid half, when will it be taken off my credit? And will my score go back up or stay the same? Please help, I m panicking.