Building my credit score

Ive tried everything to build my credit score. All of the accounts that I have open are paid on time, but do not report my credit. I have tried to get credit cards that are known for building credit, but am always denied because I don't have enough credit history. As well as my bank. The only thing on my credit is my student loans, which have on time payments, and a medical bill for $63 that I have tried to settle with the office, but they say my account in closed. Ive contacted the collection agency and have been told the same thing. Idk what to do at this point. Any suggestions?