Your reproductive doctor should be going over the process with you so you can make educated decisions.
First of all, they would start with a sperm analysis, and then move on to testing you. An HSG is relatively invasive, so you would want to do the blood tests, ultrasound etc. before having the HSG done. Blood tests and u/s will determine whether or not you ovulate, and whether or not you are producing the proper hormones to maintain a pregnancy.
I had an HSG which revealed that my left tube was blocked. For me it was quite painful, but I've spoken to a lot of other women who said it wasn't painful at all.
I was able to become pregnant with a blocked tube, it just took a little longer.
Hope this helps.
EDD: Sept 11th