If nausea starts going away after have missed two doses of fluoxetine does this mean it's medicine or what?

It's possible: But remember, fluoxetine has a very long half life. If you have been taking this medication for awhile, it's half-life is on the order of 4-6 days. Which means it won't be completely out of your system for on the order of 20 days! So missing a dose or two, might suggest some contribution of nausea from Prozac but not necessarily. Review your concerns with your prescribing doc.