19 and ttc- am I pregnant?

My next period is due around 8 days from now, I took a test a few days ago and got a partial after it sat for 24 hours. Now, I've taken 3 tests and all have come back completely negative. 
I feel so heartbroken that I might not be pregnant when we thought I was. I'm having all the symptoms: tender nipples, larger breasts, exhaustion. What is going on? Could I still be pregnant?