Salute to you for taking credit seriously at such a young age. If you manage it properly from now on, you will have a lifetime of opportunity in front of you. As for your question, if it were me, I'd try to handle the Amex issue while also establishing positive history. Depending on how recent the Amex c/o is, it's likely you'll have a hard time being approved for prime unsecured cards so you'll need to consider another route. I'd look to add another secured card, secured loan, or maybe a New Coast Direct account or similar. (preferably one that doesn't hard pull) Perhaps consider establishing a relationship with a local credit union. They're usually more lenient than the larger banks and tend to cater to the needs of their customers.
Think of it this way, while you're working on cleaning up the Amex situation, you will have another account reporting more positive payment history for as long as it takes. Something to consider. Good luck
Starting FICO 8s | 06/2018: EX 601 ✦ EQ 605 ✦ TU 590
