surelynotcani - I am confused as to when you think you might have become pregnant?
Are you thinking you have been pregnant from before your first post which was nearly a month ago from the sex on the 20th August.
Or do you think you became pregnant from 6th September?
IF you are thinking that you are pregnant from the 20th August you must guess you are about 8 weeks pregnant, if so, pregnancy tests in later pregnancy can show up as false negative due to the hook effect, where the hcg can be so high that the test malfunctions, you would need to have blood test or scan to confirm pregnancy in this case.
Also what did the doctors say from your test on the 7th september? Was it a blood test and did they say it was negative then - if so, then this must be a new pregnancy from after that time surely?
IF you are thinking that you are pregnant from 6th September you are only going to be around 5 weeks pregnant, possibly only around 4 weeks pregnant, which would explain the faint tests. In which case I hope you were intending to get pregnant having stopped the pill!
Did the result on the test that you took yesterday come up within the time limit and have colour in it?
Sorry to read that this has been going on for you for over a month and you still have no answer. I hope you get an answer soon (my mum and sister both had pregnancies where they did not have positive pregnancy tests, and it is stressful)