I had my tubes untied in march and I'm still not pregnant what am I doing wrong

You are doing nothing wrong. Tubal reversal does not guarantee pregnancy. It is quite rare to become pregnant after a reversal.

I have to wonder why your doctor did not explain this to you.

March to August would not be an unusual amount of time for a healthy couple to become pregnant. However, if you had tubes reversed it could possible take longer or not be successful at all.

If you're unclear to your personal situation, schedule an appointment with your doctor to discuss your concerns.