Switching SSRIs

I have been switching SSRIs from Paxil CR, to regular paxil, to Zoloft and now i am on Lexapro.  There has been about a month in between each.  The reason for the switch is that i cannot take the headache these cause.   I was once doing pretty good on Paxil but not anymore.  My question is, when will i feel better?  I have been on Lexapro for almost two weeks and although i do not experience withdrawal per se i wonder if whatever therapeutic good i obtained from zoloft will carry on to Lexapro or will i need to again start counting from the first day i took Lexapro?  I read that most SSRIS take about 2-4 weeks to be effective, but what when you have been on one or another over the past 4 months?

[Roger Gould, M.D.]

The month lapse in between is what causes you to start allover again from the beginning each time.. There may be a residual effect from the last round, but you can't count on it because all the medication has been out of your system for weeks.

[Rutegaard]

I got the impression Torreja has been switching every month or so, medicating with some SSRI for the past couple of months.

[Anything4Money]

Earlier this year (2005) the American Psychiatric Association admitted that no chemical imbalance causing mental illness has ever been proven.