Mary,
Welcome home!  Glad to see you back online.

I wonder about a couple of things.  If baby has a receding chin and is
sucking in his lower lip, he may be keeping his tongue behind his lower gum.
 His gums could be causing the red mark.  I think it may be difficult to
correct the poor suckling after 2 months, but putting baby in a sitting up
position and being persistent in tucking out his lower lip should help.

Check under the baby's tongue.  If he has a short or tight frenulum, he may
not be able to get his tongue out over his lower gum.  That may also be a
factor.

I wonder if the red mark could be from muscle spasm, tho we usually think of
a blanching, whiteness in relation to that.  The pain you describe sounds
excruciating.  Let us know how things work out.

Jeanne Fisher
Austin, TX