I had unprotected sex on the 24th of June but the next morning I took the morning after pill. The doctor prescribed me the pill but I couldn't start it till my next period which wasn't due till around the 15th of July, but on the 29th of July I had one day of bleeding so I started taking the pill (because I thought my period had started). My doctor told me to go back if I had not started my period by the 20th of July to do a pregnancy test, and since its now after the 20th and I have not had any more bleeding since that one day, should I go back? However I am not sure if that is due to starting the pill which has messed up my period.

It's likely the bleeding that you had on 29 June was related to having taken the morning after pill.

Since you started your pack of pills, your cycle will now alter the week you are taking the hormone free pills. See what happens on your off week.

You can always try a pregnancy test for the peace of mind.

The one issue is that the morning after pill may stop or alter your cycle for one or two months. (one of the listed side effects).

So there is no way to tell at this point, starting the pills at that point, your body will have to adjust to the changes(but it will)

It is doubtful that you are pregnant, but it is possible. You need to wait and see if you get your next period.