Credit score confusion (self)

[Andy Ballester]

I had just recently applied for a mortgage loan, but had not checked credit score in about 8 mths, however last time I checked score was a 705 on all 3 agencys, after applying I had only checked with experian assumed may be a little better, only to find out my credit score was 635 I have some school loans which I have missed some payments in distant past, have not missed a payment in 4 yrs only owe about 4800 left, 3 seperate loans required to pay 100 mth and I pay 125, and one other outstanding dept it is to a bank, for a previous closed account, which I owe 215$ it was from 09 for a 1$ overdraft which they kept billing me 30$ a day for a week before I was notified needless to say I was extremely upset and closed account, I know stupid I should of taken care of it and will as soon as posable. Im also a merchant marine so I basicaly live on the ocean I have 15000 in a thrift savings plan and 40000$ in cash assets no home, no car payment, no credit card debt, honestly never had a credit card. And there is no new dept on my credit report, how could my score drop 70 points and if I pay off school loans in full how long and how much could it rise. What is my next step I could have zero debt tommorow. But not sure how much it would help suggestions please.