I agree with everyone, you should have the HSG done before proceeding
You want to make sure there is absolutly nothing in the way of your future treatments. I've had one done AND I also work in radiology where we do them often. One a personal level, mine was quite uncomfortable. I believe it was due to the physician's lack of experience doing them. She couldnt get a good seal and the dye kept draining out. 45 mins lator she was finally able to do so. Typically .... the whole procedure take's 10 to 15 minutes. Most girl's have a lot of cramping, especially if the tube's are blocked. As far as allergies to shellfish, the HSG doesnt really apply to that guideline. We use a lot of dye ( Isovue ) that is higher in iodine, so chances are if your allergice to shellfish, you'd have a reaction to a product with iodine.