Citalopram was Celexa. Lexapro (escitalopram) is one of its breakdown products.
1) One needs to take twice the dose of citalopram to match the strength of escitalopram. Someone on 10 mg of Lexapro needs 20 mg of Celexa to match for strength.
2) Generic meds are often trash, and result in much lower body blood levels, even after matched by dose with the brand name drug.
3) Although chemically related, some people respond well to one, and have no response to the other.
You should review the changes with your doctor. If increasing doses does not help, the doctor should call up the insurance company to get you back on Lexapro. They will refuse because they care only about money, not about health. The doctor might have to use curse words and threats to get you what you need, stay on the phone for an hour.
I hope you appreciate that.