How to raise my credit score from 565 to at least 620 in two years?

Right now, my score is 565. My fiancé is in the military and has 2 years left. Once he gets out of the military, we plan on getting a house (we will be married by then). We are looking at the VA home loan, but you have to have a score of at least 620. My fiancé is in the 700's, but unfortunately, because of my past mistakes, my score is sitting at a 565 right now.
I have a student loan that is in collections right now, but I am now playing that off on time, monthly. At this rate, I should be done paying it off in exactly two years. I heard that once an account in collections is completely paid off, I can cause the score to drop. Is this true? That's because why you make a payment, the last activity on the account becomes more recent, making it weigh more negatively in your credit file, is what I heard. I will be done paying it off around the same time we plan on getting the loan. I am confused about what to do regarding this.
I have a credit card that I have been making payments on time. If I make payments on time for 2 years and keep below the 30% threshold will my credit increase enough to the 620 I need?
Also, I have another student loan that I have been making on time, monthly payments. Hopefully this helps too.
I would like advice on how to raise my credit score over the next 2 years with what I have going on right now.
Should I get a secured credit card down the road and keep it below the 30% threshold? Will opening another account help?
Thanks in advance!

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