I'm switching from lexamil to fluoxetine cos I can't afford the lexamil anymore, and can get latter for free at the hospital. Am I going to experience withdrawal? I can't wean off since I can't buy it

No. If you mean Lexapro (escitalopram) rather than lexamil then no. Lexapro (escitalopram) and fluoxetine are both ssri's and changing to fluoxetine should not cause withdrawal.
Probably not. Since they are within the same class, direct switch wouldn't cause withdrawal, there is a slight. Chance that you may have different effects or side effects, it's hard to predict . Discuss with your doctor.