I take 20mg escitalopram dr said i could go up 5 more when i went to pharmacy he said it could cause serotonin syndrome don't know what to do?

Don't panic: Is "he" who mentioned serotonin syndrome (SS) the pharmacist? He's covering his backside. You should do a web search for SS to familiarize yourself with it. It's EXTREMELY rare and though it's said to be life-threatening, it can also be mild. The likelihood of your developing SS by going from 20 mg to 25 mg/day is not zero, but it's close to zero. But reassure yourself by calling your doctor.