I sometimes get a sore spot in the rhomboids-
it's more like under the edge and very close to the scapula vs a more surface muscle pain from the traps.

The rhomboids are pretty much a weak muscle and can get overstretched easily by a forward shoulder posture.
at least that is what causes mine to get sore spots- as soon as I work a few times on keeping my shoulders back that soreness goes away.

I can't remember what site I read that info on - but if you think it is your rhomboids don't try to stretch it out.
do the lay on the floor things like Victoria mentioned just on the floor or with some sort of roll, depending on how it feels for you.