Why no longer iron shots, to instead of iron infusions?

With Crohn's, I ve been iron deficient since 17. I'm 66 now and my iron is low and the infusions don't do much..1 then 2 weeks later #2.
For yrs the Iron shots, given in buttocks top, were the best, as I felt so much energy and stronger and lasted 6 months. The only issue was brown spots on skin where shot was given...who cares! I'm on B12 shots 2x a month but it's my iron that won't stay stable..Anyone know why they stopped iron shots and how can I get them again? Thnx