Needing info about HSG test, please!

I'm supposed to have the test at the start of my next period. I have no clue what to expect. The last time we tried to schedule, I had started my period on a Saturday. My husband and I had sex on my second day, and I called on that Monday when the clinic opened but they said I couldn't schedule because we had sex even though no one told me beforehand not to. No one has given me any information about the scheduling, how it will be, or when in my cycle they will do it. I can't get much info online either. Can anyone help??