How long do Braxton hicks last?

I've been getting what I've assumed are Braxton hicks for a few weeks now, but lately it's like continuous pain in the evening that doesn't let up. I always thought they were like contractions, with a peak then gradually tapering off... Just curious what others have experienced! Mine are lasting for several minutes at a time at least, with sudden pangs I assume are peaks but they haven't really let up so I can't really time them or anything (can't figure out the start or end!). Thanks!