It sounds sort of like you've been riding this seat for a while, and it's been fine, and now it's a problem?

Is there something else that's changed recently? Have you had the bike in the shop?

(I had my bike fixed from a non-seat problem, but they move the seat to clamp it, and left the seat about half an inch higher than it was before. It took me a while to figure it out because it wasn't a huge change, but lowering the seat back solved my soreness at once.)