5 Days Late Negative Test

Ok ladies! Need opinions! We have been TTC for 15 months. This month I was due to start 4/11. It still hasn't started and no normal cramping like usual to show it is coming. I have took 3 test (day period was due, 2 days late, last night 4 days late) they were all negatives. I have started getting car sick and tried touring a battleship with the family and got sick on it. Not normal. Nauseous in the mornings and some times near bed time. Trying not to get my hopes up but something seems not normal this month :). Could I still be pregnant and when should I test again?