I am slowly repaying every loan or past due notice I have ever had. Some of them are settlements. How long after clearing these and being on time with my payments does it take for my credit score to start going up? I was terrible in my youth and am trying to fix all of that but my score doesn't seem to ever change. I want to buy a car and not pay double the asking price to a finance company. Any advice is greatly appreciated.

It takes years to clear up your credit, bad postings can show up for up to 7 years ( bankruptcy 10) In the settlements did you deal with them to take off the negative on your report as part of the settlement ?
But as you pay and they get older, the credit score keeps going up and up, it just takes time.

First make sure that the information shown on the reports from all three bureaus is correct. The site to get all three for FREE is: www.annualcreditreport.com/cra/index.jsp . If you want your scores, there is a charge. Often when you pay off a collection or charge off, the creditor fails to report this. Such errors can be disputed. If you have no good recent credit to offset the bad, you might consider getting a "secured" credit card. Try not to use more than a third of the credit limit and pay the balance off every month. That way you won't be paying the high rate they charge. After a reasonable time, you should begin to get offers for unsecured cards. At that point you can request your security deposit back. If they refuse, you can cancel that account and open a different one. Your efforts to fix your credit will be well rewarded.