there is a flush draw on the flop? It is helpful if you post the exact cards.

Let's say you have Ts9h7h5c and the flop is 8s6s3d

The first step in evaluating this draw is to determine how many nut outs you have.

three fours, two fives, two sevens, two nines and three tens.

12 nut outs in this example. It is very important that you have the nut wrap, as non nut outs must be treated with extreme skepticism in multiway pots. Whether you have a backdoor flush draw or not is also important, especially when stack sizes are much deeper, because in the example I have posted you could easily be drawing to get freerolled. OTOH because you have the nut wrap you will have a small free roll yourself on say the 5h as you can go higher.

We know 7 cards, so there are 45 remaining. We like 12 and dislike 33. Slightly better than 3:1 against hitting your draw on the turn (2.7:1 against hitting or w/e I am estimating). You are getting 2:1. So it is pretty close. The button could raise, although your equity probably wouldn't be that bad three way anyway, and you are not deep, so that is not really the end of the world.