Hello,
These can be the symptoms of pregnancy and the brown spotting can be due to implantation bleeding or corpus luteum defect. However to confirm the status of pregnancy, I suggest you to test for pregnancy by a highly sensitive pregnancy test 10 days post ovulation with a sensitive ( 20 - 25 mIU ) pregnancy test. Also then I would suggest you to get your serum HCG levels estimated since this is more specific than urine for pregnancy tests.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
I agree - I think your test on the 2nd was a little early. I'd wait until your period is due and then test again if it doesn't show. As for STDs, it might be worth getting checked since you had unprotected sex. I'm not sure how quickly all STDs show up on tests, but you could talk to a doctor or STD clinic to find out the time frame for when you should have testing done. Keep us posted if you take another test!