I get that way. As soon as I start to cum it gets very sensitive and I have to slow down. It's almost like being tickled it's soo sensitive. I've found that if I'm very very aroused I can sometimes keep going without getting too sensitive, and it feels ohhh soo much better. I've also found forcing myself to keep going has sort of desensitized myself a bit which is nice.
But as for being sensitive after. My ex gave me a bj after already cumming...I couldn't take it. It was like someone was tickling me. My legs were freaking squirming and was WAY too intense, and went nowhere.