I have pcos and cannot know if my period is late I took 2 tests both negative. I have nausea dizziness and sore breasts. What can this be?

Premenstrual. If you have had negative pregnancy tests then it seems more likely that the sore breasts are due to cyclic hormonal changes and as for the dizziness and nausea it is possible that these are unrelated to the breast tenderness. If the dizziness and nausea is severe or persistent you should see your doctor.