What’s the fastest I can get my diploma?

I want to join the Military and need a diploma to do so. I feel stuck in my town and need a way out to better my life. I live in Indiana US also. I have 23 credits but it’s summer time and need a online school that I can get all my credits all at once within like 2 months. I’m 19 also that should be mentioned. I need something I can just grind out with every second I get, I just need it as soon as possible.