Had sex all during ovulation. now 4 days late for period. neg hpt. dizziness upset stomach headache and period cramps that come and go. could it be?

May be too early: Some hpt's have variable sensitivity. The hormones that cause the test to tern positive may take a while to build up enough to be detected.The first morning urine is generally the most concentrated and more likely to reflect your condition. I would just test again later.

Yes, it could: Sometimes home tests are not reliable so have a test done at a doctor's office or family planning clinic. Blood tests are more accurate and - if that is also negative - they'll be able to start discovering what might be going on. It sounds like you are trying to conceive - if so, best wishes for a positive test and a healthy baby!