What Causes Recurring Nasal Crusts?

I had transsphenoidal surgery to remove a pituitary macroadenoma in July. I had regular follow up visits with my ENT where nasal crusts were debrided. After each of these visits, the foul smell would return within a few days, indicating that I needed another debridement. After a few months of visits to the ENT, he told me I was completely healed and did not need to be seen again. However, I continued to have the recurring nasal crusts and foul smell. After two more visits, my ENT told me to use the NeilMed Sinus Rinse. This has helped for about a month and a half. Each time I started have a foul smell, I would do the rinse and be able to expel crusts afterwards by blowing my nose. Now I can feel that I have crusts and the foul smell has returned but I have done the nasal rinse multiple times with no results. In my last two visits with the ENT, he has not been able to offer any reasons why I am continuing to have these crusts and he was surprised by the amount of crusts he was taking out. What are some reasons that I would continue to get these crusts? (Some additional information – My ENT told me prior to surgery that he felt I had seasonal allergies. Also, I am now 17 weeks pregnant.)