Big Unimproved Pair on Fifth Street, Caller Raises

[parappa]

A very common situation that I run into (sorry, Crypto 1/2, ante 25c) is that I have a big split pair, like (xA)A, and complete the bring in on 3rd. One person calls. 4th street, we both catch blanks, I bet, they call. 5th street, we both catch blanks, I bet, they raise. At this point there is usually about $12 after their raise. It costs me 2 to call and 6 to see a showdown where the pot'll be 18ish.

This feels to me like the situation where you get check/raised on the turn in hold'em--I feel like the raiser is telling me he's got top pair beaten.

I've been folding this on boards where I see a 3-flush or a 3-straight, and I'm not very upset about this, though I'm not certain that it's right. It's when the other player's board is complete rags and he raises that I get confused.

I've been calling down but I feel that this may be a leak, and that I maybe should be routinely folding here. I looked through old posts and the archive here and I haven't been able to locate a concrete answer. I know that this is very situational but it takes me some time to figure out how many outs I have vs what he might have, how many cards are left, etc. and I'm not quite able to estimate my odds very well just yet. I'm looking for some general ideas that I can adjust for specific situations.

Thanks!