implantation bleeding

Brittany • Mother of 2 boys( 6/11/08 and 7/4/17) DH had vasectomy, IVF fresh cycle #1 BFP November 2016, Baby born Independence Day 2017, can't wait for baby #3 in a few years! 👶🏽💙❤️💙❤️
I am 4dp5dt and last night I noticed a light brownish spot on my panty liner. This morning I noticed a pinkish sticky discharge when I wiped. Could this be implantation? Or a side effect of the PIO and estrace?