Can you get a loan with a 615 score? Yes it's possible. Are there be better terms if you can improve your credit? Very likely there will be. Are you in a rush to buy? If not, then getting to a 640-660 will open the doors to a lot more lending sources, not just Wells Fargo (FYI never just go to a mortgage lender company or mortgage broker company.... always go to an individual loan officer who has been recommended/referred).
Were you on periodic unemployment during the down times last year? If so, that is perfect documentation to explain the lower income in 2010, and will go a long ways to getting 2010's employment income extrapolated over the time you worked (so if you made $49k over 8 months, it'd really be $73.5k for the year).
You said you made $65-68k/year in a normal year (before last year when it was bad), but you are now on track to make $90k this year... why are you on track to make nearly 50% more than you did in years past? Pay increase? Lots of OT?
Are your medical collections the only negative items on your credit report? Or are there late payments, non-medical collections, etc.?
What were you eventually planning on doing with the medical collections? If you were planning on paying them, read http://whychat.5u.com/hipltr.html
before you do. Medical collections aren't a big issue when it comes to qualifying for a mortgage however... but keep in mind that medical collection agencies can mess with your credit by illegally randomly "updating" the date of last activity (DOLA it the common acronym) in an effort to get you to pay them (the worse they are hurting your scores, the more likely you are to pay them... so they think). Perhaps they already have, as 615'ish scores usually indicate negative marks within the past 24 months.
Getting your credit card to report as a $0 balance before lenders check it (this means paying it off and not using it for ~30 days) will give you a credit score boost, the higher that utilization % is right now the more paying it off will increase your scores.
How long have you had the credit card and 2 car loans for? If they haven't been very long, then you may not have a lot of "good" credit to offset the balance on the revolving credit card + the medical collections from 4-5 years ago.