HSG vs. SiS

Hi, which test is recommend for me to do an HSG test or an SIS test? I've been trying for 2.5yrs to have a baby. During year 1 I actually got pregnant twice. The first pregnancy was a stillbirth that I lost at 22 weeks and 3 months later I got pregnant but then lost that pregnancy at 10 weeks. So for 1 year now ive had no pregnancies and have been trying. I even did 4 IUI's within this past year and have failed. I know I have fibroids but I am trying to figure out if it maybe something else too maybe endometriosis? One obgyn told me to do an hsg test, the other told me to do a SIS test. So I wanted to know which one was most effective for you? Or should I just do both?