Your Dad should get some DNA tests done
I'm the spitting image of my dad's youngest brother (medium height, light brown/blonde hair, green eyes) while my dad is tall, black hair, and brown eyes.
for years I was really convinced that my mom had an affair, but the timeline just doesn't match up because my uncle was deployed overseas during the years before my birth. I just chalk it up to genetics being screwy.
I think I got all the physical genes from my dad's paternal side, because while my dad bears a striking resemblance to all the guys on his mother's side, I look exactly like my other uncles, grandfather, and his brothers too.