Switching Birth Control - question

Na
Hello Ladies,
I recently switched birth control from Sprintec to Gildess 1/20 (which is the same as Loestrin 1/20) because I was suffering tremendous mood swings, paranoia and anxiety and almost borderline depression.
I feel so much better and I'm almost back to my perky self.
I just wanted to know how soon a new birth control pill becomes effective if you are switching from one to another. My doctor said it could take a few months but I wanted to hear what you guys have to say.
Thanks!