Just like jnitro said, the test is not painful but unpleasant. It's very quick and you will know results right away. Also, many people believe that HSG improves probability of BFP since it cleans out your tubes.
Good luck!
I had an hsg test done about a month ago. and it wasnt painful just uncomfortable. it is very similar to a pap. they use a tube to inject dye to see if your tubes are blocked, and you can watch it on a screen, when they inserted the tube it casued cramping and it was over in like 10 minutes. dont worry its not that bad.