Hi Heidi and welcome! In answer to your question -- NO, it's not given that you'll gain weight with hypothyroidism!
I don't think that there's any reason why you would become hypothyroid and
not be treated for it -- and
untreated hypothyroidism is what could cause a weight gain. You're undoubtedly under a doctor's care for your condition, right? -- he/she will continue to treat you until your thyroid levels are normalized and into the future.
I imagine that you will need to take a synthetic thyroid hormone replacement (like Synthroid or Levoxyl) for the rest of your life, like most of us do. At first, you'll probably be started on a small dose and your thyroid levels tested every six weeks or so until you are in the normal range. Then you'll probably be checked every six months or so (this is the schedule that I'm on).
My doctor told me that so long as my TSH levels were in the normal range, I should be able to lose weight normally, which is in fact what happened. My Levoxyl dose needed to be changed as the weight came off and continues to be tweaked every six months but I'm still successfully maintaining my loss.
Many people with hypothyroidism find that a lower carb diet, emphasizing whole grains, fruits and veggies as carb sources, works best for weight loss and maintenance.
Congratulations on losing the 60 pounds! My opinion is that if you keep doing what you did to lose those 60 pounds, you won't see a regain. Once you get your thyroid normalized, I'm sure you'll be able to take off those last pounds.
BTW, my daughter just moved to Albuquerque and I LOVE your city!