Like MLP said, UC does not "become" Crohn's. It's likely you were misdiagnosed with UC when in fact, you had Crohn's.
Anxious855, I have just read this entire thread and the first thing I wondered was whether you are seeing someone for the anxiety? Anxiety makes everything worse. It makes you more aware of physical symptoms and can make pain worse. Have you seen a psychologist and tried Cognitive Behavioral Therapy?
My daughter deals with anxiety too and has been working with a psychologist for years. Her GI insisted on her seeing one when she was diagnosed. Said stress would make the disease worse and my daughter needed to learn how to cope with a chronic illness.
She sees her psychologist regularly and has learned several techniques to calm herself - diaphragmatic breathing, guided meditation or listening to audiobooks. There are several apps she likes - isleepeasy is one and Headspace is another.
Coping is hard, but not impossible. What you are doing now is called catastrophizing - imagining the worst possible outcome. That doesn't help anything! It's really hard not to do, but I would suggest thinking about the best possible outcome. Because if you think the worst could happen, then the best could happen too.
The best possible outcome here would be you going on 6MP and it working and you being in remission and getting used to your "new normal." Your new normal will include appointments with your GI and blood work every 3 months, but besides that, it's not all that different from your old normal! I prefer thinking about that outcome, don't you?
CBT teaches you to look at and respond to situations differently.
6MP or Imuran (Azathioprine) do require frequent blood work in the beginning, but once you get past that, it's every 3 months and you don't have to think about it. It's weekly for 4 weeks, biweekly for awhile, then monthly for awhile and then every 3 months.
It does take a while to work, which is why you are put on steroids usually, to induce remission while 6MP kicks in. EEN is another option. It is standard for kids in the UK, and I know sometimes adults do it too. It actually heals better than steroids do. It's formula and nothing else for 6-8 weeks. It is hard, but possible.
Besides like 6MP and Imuran, there is Methotrexate. Then usually Remicade, Humira, Entyvio, Stelara, Simponi and Cimzia - you have LOTS of medication options. I really think you need to try not to panic, because you WILL find the right medication and then you will barely think about IBD!