Welcome to PC! Sometimes drugs like Prozac cause withdrawal symptoms so I think three weeks may be a little soon to go back on but it's best to ask your doctor. Like Skeezyks said, it is highly individual. I was on 60 mg of Prozac for a couple of years, which is a high dose but I'm a rather large person. I ended up switching to Zoloft for a few months and then went off anti-depressants altogether. I didn't have many withdrawal symptoms but was only on it for a couple of years and you were on it longer so there's a greater chance of you getting withdrawal symptoms.