Spotting and "flu-like" symptoms

Ok ladies, here it goes. I'm not on birth control and only use the "withdrawal" method (if you cosider it that.) I've been tracking my periods for years and run pretty consistent cycles. 31 days with spotting 4 days before starting followed by 4 days of actual "flow". PMS symptoms typically the same: bloating starts the week before, cramps are awful and typically a back ach or two. However; this month was different.. I didn't even realize when my period was supposed to start until I decided to open my tracker app. This past Monday I was scheduled to start. Instead I had light spotting.. Now it's Friday. Still very light spotting (as in, I only see blood when I wipe after going to the bathroom). Today I developed a low-grade fever (99.8) and am having flu-like symptoms. I rechecked my tracker app and noticed that I had sex the day before and the day after ovulation. Obviously I wasn't thinking, because I never do that! Pregnancy test this morning was negative, but considering the facts I would only be 2 weeks pregnant (if I am). Is it still too early to test or should I trust the negative? Thanks for the help!