Try to negotiate to change to a part-time position at the same company you're at right now. Or start looking for a different job elsewhere which will give you part-time hours, which will free up more time for you to work on your side project while also having a stable supply of income for yourself/your gf.

In the mean time, I believe you need to revamp your diet and keep up with your gym activities. If you eat well and keep working out, you may become strong enough to handle this current workload and still be able to work on your project.

I wish you the best.