You don't need to work in a lab with a PhD in Chemistry. You have a ton of other options. I'm envious of your position. You can go into education, consulting, chemical sales, patent law, government policy, etc. And you're getting paid to goto school, right? Earning a $25k stipend per year vs. paying $35k in tuition at a pharmacy school is a difference of $60k per year. It's not worth the 1-3 years it'll take to re-take courses and 3-4 years in pharmacy school.
I can't answer your question adequately because I don't know how many classes you have to retake. But it sounds like maybe a year. If you're trying to figure out when you'll graduate with a PharmD, this should give you an idea. One year to retake pre-reqs and then apply to the 3 year pharmacy programs. If you want to specialize and do a residency, that could add 1-2 years. Realistically you could graduate anywhere from 4-8 years from now, but I'd bet on 5-7 years.