Reddit mentions of Medical Spanish, Fourth Edition (Bongiovanni, Medical Spanish)

No single resource will do. Find a few different ones that you like and stick to them. Memrise will help but only as a supplement, not on its own. It'd also be a good idea to find someone to talk to about the language and gradually in the language instead, as your Spanish gets better. Lucky for you there are a ton of us Spanish speakers in the world, and it's one of the most popular languages to study. A quick search on here or /r/Spanish will help you find the resources people like best.

Ideally you could also get a textbook like this (first ones I found on google, cannot recommend or not recommend) http://www.amazon.com/Spanish-Medical-Interview-Textbook-Clinically/dp/1416036490 or this http://www.amazon.com/Medical-Spanish-Fourth-Edition-Bongiovanni/dp/0071442006/ref=pd_cp_b_1 that will help you learn the medical vocab you'll actually need to know along with the language.

If you want to get a book (which is generally cheaper than courses), I've read this one and it is good:

http://www.amazon.com/Medical-Spanish-Fourth-Bongiovanni/dp/0071442006/ref=sr_1_6?s=books&ie=UTF8&qid=1453634368&sr=1-6&keywords=medical+spanish

I also think the most important things to do are:

1. Use multiple senses - talk out loud, listed, and read
   
2. Interact with other speakers, even if you're scared
   
3. Make a schedule and stick to it
   
   You could spend only 15 min a day and still progress if you're committed. Good luck!

Practicing will obviously work the best, maybe volunteer at a clinic more likely to have spanish patients?

I think this is the most helpful medical spanish book: http://www.amazon.com/Medical-Spanish-Fourth-Bongiovanni/dp/0071442006/ref=sr_1_6?ie=UTF8&qid=1464016441&sr=8-6&keywords=medical+spanish