Hi Kafina,
Its understandable to be worried whenever your period is late and you are sexually active, but seeing as you’ve had pregnancy tests in the last 2 months I wouldn’t worry too much. Spotting can be a sign of pregnancy, but usually its just a symptom of irregular periods, which it sounds like you are having and is perfectly normal.
Maybe if you are still concerned it would be best to buy a 2 or 3 pack of shop pregnancy tests, and you can always do one just if you get worried, and save the rest for another time to put your mind at ease.
From what you say, it’s probably unlikely that you are pregnant, but in the end the only way to be sure is to go see your doctor or do the home pregnancy test thing above. I don’t really think there’s much cause for concern though 🙂