Exactly that!
Teen daughter had cold symptoms, tested negative day 2-3, was up & down (feeling better, then feeling worse over the next few days) As not picking up day 5-6, tested again Saturday, and it a very quick positive!
I have had sinus headaches all week & today sore throat - negative LFT but seeing dad tomorrow for his 90th birthday!
Wish I knew for definite if this covid or not .