Anyone be able to help?

I am trying to figure out my due date...
*My last expected lmp was 1/17 
*I had unexpected bleeding for 3 days and was light from 1-31-2/2 (normally my periods are light big last 4-5 days)
*My BFP was 3/14
What should I use for my lmp to determine my due date? I don't have an appt until 3/25, which I will know more then, but trying to figure this out. Any ideas?