text: This is going to sound weird, but it absolutely works: Put some ice cubes in there, and don't piddle around about it (make it quick).  It will shock your muscles into tightening up, which is what the problem is.  During sex the striations of your muscle walls in there are are spread apart and loosened up (especially after a climax), and that entire area becomes more vulnerable to friction issues,  which is what's causing the agitation you're experiencing.  Simply shock those striations and the skin over them into tightening up, and you should instantly feel a lot better.