Wow. I would do a lot of research and discuss with your doctors (both GI and GYN) before doing this. I believe that the harvesting process is invasive, and involves messing with your hormone levels to get your body to release multiple eggs, so it's not something to do lightly. Also, insurance might not want to cover it, considering it's for possible future pregnancy and not current infertility. So it's going to be expensive.
It all depends on the severity of your disease, but women with Crohn's have healthy babies. I can understand the concern, the meds can really mess with our bodies. It wouldn't hurt to consider your options. But you're only 17. Don't let them push you into doing something you don't want to do. It's your body and any elective treatment like this should be entirely your decision.