My doctor prescribed me sertraline hcl 100mg 1 a day and venlafaxine hcl 75mg 1 a day, but i'm reading here its not good to take both together, i have deppression and anxiety really bad for many years i feel sertraline is not working any more?

You are correct because there is a major interaction when taking both together even both are not at maximal doses yet. I wonder if your doctor wants to replace sertraline with venlafaxine because sertraline is no longer effective. However, these 2 medications are at times used in combination but for your peace of mind you should call your doctor for confirmation. Good luck.