Confused...

So according to this app I'm 18 days late. According to my Fitbit app (which was more accurate this last cycle) I'm 9 days late. My breasts are tender and I feel, not a pain or cramping really, but something in my lower abdomen. I took a test the day I was late (according to my fit bit) and then again 4 days later. Both said not pregnant. Advice on if I should keep testing or not? I have 2 children already but we weren't trying for them at the time. Now that I'm consciously trying, am I blowing symptoms up to be more than they are? Should I be concerned that I've been off of my birth control and have been trying since December of 2018?