It could be the multi function switch, yes; but those are quite pricey. If all the fuses are fine, and all the bulbs are fine, the usual culprit of turn signal malfunctions is the turn signal relay, the little box which makes the iconic 'tick, tick - tick, tick'.
These do go bad from time to time, and they're much cheaper than a multi function switch. These can be found on rockauto and should be available at your local auto parts store.
The turn signal relay is going to be in one of two likely places. Things started changing in 04 so, I can't say for sure. One, it's up under the dash, towards the radio in a black box with other relays. It's likely a colored relay of sorts, like blue or yellow.
If it's not there, then it could also be on the passenger side in the SJB (Smart Junction Box), located in the passenger footwell where other fuses are found and possibly other relays.
Or, instead of hunting around for it, you could turn the turn signal on (engine off) and use your ear to look for it.