Had Unprotected Sex. Negative Pregnancy Test. Now Dizziness. When Did I Conceive?

anon hi im really confused because I had unprotected test while on my period on the 20th june and then again on the 23rd june my period had stopped on the 21st that was my last period. wen I done a test a week later at the clinic I wwas negative I had done too more tests before the clinic on the 24th june still negative then I had unprotected sex again wiv someone else on the 27th june but I took the morning after pill I went on holiday on the 2nd august I felt really sick and dizzy I done two tests on holiday one was negative and one was positive wen I came back on the 9th aug I was positive then I went to the clinic on the 23rd aug I was positive im now 13 weeks and 5 days. wen would I have conceived I cant work it out.