Late period. Tested negative. Confused.

My last period was 9th-16th Jan and expected the next period to be 7th-13th Feb. I am sexually active, using condoms majority of the time. I have taken the pregnancy sticks twice, turning out to be both negative. Usually, I would get sore breasts and light cramps before I get my period but I have no period symptoms at all at the moment.  
Also, I went swimming during one of the last days of my previous period, using a tampon (I haven't used them for years). A few days later, I got badly sick with fever, chills and feeling nauseous for a week long, assuming that it is toxic shock syndrome??? Would that sickness delay my period?