I did a quick covid test on 12/31, it was negative, even with a high temperature, today the 4th i did it again and it was positive, how do i know which day i am and if i can get worse? i didn't have a fever, just a slight cough?

Count day 1 as the day your symptoms first appeared. Your original test may have been negative because transmission peaks between days 5 and 7. After day 10 the transmissibility decreases and you can end self isolation. Airlines and international travel may require 14 days from your positive covid test.

The rapid antigen test is only 50-60% sensitive but it is highly specific (95%) so the first test result was a false negative test and the second test confirmed the infection. You had fever on 12/31 so you have had the infection since then. You no longer have fever so it is a good sign. By CDC, more than 90% of cases in the US are caused by Omicron variant so you are now safe.