For IUI your fallopians tubes must be open.
To check Fallopian tubes we need a diagnostic hysterolaparoscopy, wherein a telescope is put into your abdomen from your belly button, so as to check the exterior of your uterus as well as the external opening of the Fallopian tubes.
Additionally, we have to do a hysteroscopy as well, that is putting a telescope into your vaginal opening and then having a look at the inner lining and the internal opening of your tube.
If your tubes are normal then you have unexplained case of infertility, and same has been observed in few instances in past. Sometimes there are no reasons for infertility as such, but this can be concluded only if your reports and that of your husband's turn out to be normal.
If you are overweight then you should also follow a healthy diet & exercise routine.
After doing all of this you can go ahead with IUI, if at all you have unexplained infertility. It can be done for 4-5 cycles.
You can approach any doctor from this page - Ivf doctors in India, or you can come to me as well, whichever you feel is convenient.