FEEL like peeing after sex. Why?

Sounds like para-urethral stimulation (the "g spot"). When stimulated it often eludes to the feeling of having to urine but that is not actually the case. When the para-urethral glands are fully stimulated it will lead to female ejaculation aka squirting. Yes things do get very wet. But it is completely normal and a very much sought after form of orgasm. If it happens again just go with it, it could potentially be the most fulfilling orgasm of your life; and NO you are NOT actually urinating.