12-14 credits shouldn’t be a red flag I had semesters under 12. A DO letter isn’t an absolute necessity I didn’t have one when I applied, but some schools may have different requirements.
Your app doesn’t look bad at a glance. Have you considered maybe getting an EMT cert and gaining some hands on clinical experience? Also, it could be a problem with your essays. Crafting a narrative that will make whoever’s reading your essay pay attention to you is critical considering how many apps schools get.