I had unprotected sex on October 2, this was in the unsafe period and two days before ovulation according to an app. I had very light bleeding for a short time on the 20th and it was dark. I am now 4 days late for my period and having dizziness and back pain. Tired a lot, my stomach was bloated feeling a few days ago and smells that normally would not bother me are making me sick along with mood swings. I took a test this morning and it was negative. Could I still be pregnant?

Just so you are aware... all days are considered unsafe... some women conceive during their period. Apps rely on an average... women however are usually anything but average.

So you must consider the possibility.

You are probably testing too early... the accepted period where Home pregnancy tests are most reliable is beyond the two week late point. Taken earlier false negatives become much more likely.