Could I be pregnant?

Tiana • I am 23 years old, I am married, have a 5 year old and my husband and I are having a baby boy! Due January 21,2017!
I am 4 days late on my period, normally I have tender boobs, and lower back pain when it's about to start but nothing, could I be pregnant? My husband and I have been trying for 9 months, I've taken tests and they've said negative, is it still too soon? How do I know when it's too soon? 
Thank You! :)