I took 20mg of Prozac (fluoxetine) for 4 days. I have been off of it for 3 days. How long does it take to get out of my system?

A while. Since you took prozac/fluoxetine for only 4 days, it should leave your system in about 1 - 2 weeks completely. In general, if someone has been taking Prozac for a while (longer than two weeks), it can take up to 5 weeks to completely wash it out of ones system. For side effects (or beneficial effects) to go away, Prozac does not have to wash out completely, just be low enough to not affect you.
Should be gone. There would be trace but if you only took 4 doses then it should be pretty much cleared.
Prozac (fluoxetine) Agree that it takes up to a week, usually over 72 hours of no Prozac (fluoxetine) you can feel the difference. One exception is weekly Prozac (fluoxetine) capsule which comes in 90mg. Dose given once per week, here it takes longer.