Hi - to answer your question on how to increase your credit score. Because you're currently self-employed it may be harder to get a credit card with a lower APY. But I'd still try.
Namely, here are the steps that I'd do to increase your credit score from scratch:
1. Try to get a regular credit card (Chase Freedom is a good way to start).
2. If that fails, just get one of those really high APY cards that'll just let anyone use their cards. Make sure there's no annual fees or anything tricky that'll cost you extra money though.
3. Regardless of which credit card you're able to end up with, you pay twice a month so you can 1) build up credit, while 2) have an effective 0 expense ratio (both of which will boost up your credit score), and 3) avoid having to pay any interest. You essentially want to be a "deadbeat customer" to credit card companies and pay 0 interest.
It may take a few months for your credit to start rising because without a credit card, your credit history is somewhat limited in terms of age.