Don't you just hate the "at your age" tag?
Personally, I don't think you should be going lower with your calories, you'll be starving and feeling deprived - and we all know where that leads, don't we? Maybe just walk on the treadmill until your back is better, then, could you have a couple of sessions with a PT, make sure that your lifting form is correct and that ypu're not straining anything?
Losing weight with thyroid problems is hard, I had a similar issue, went to the doctor clutching my food diary, she didn't even look at it, just said that I'd lose weight if I ate half as much and that she'd never seen a fat anorexic. Thanks, helpful.
You've done so well, awesome weight loss, you've just got to slog through this bad patch - forward, onward and upward!! :flowerforyou:

Well done for what you have achieved. As for being 'over the hill at 50' pffftt! - so speaks a delicate little lady (the doctor). It takes all kinds to make up this world - I know female firefighters in their 60's, kayakers in their 70's, even a 76 year old female fencing contractor (I'm 54). You obviously know what works for your own weight loss - and where to find help and new ideas. Listen to everyone and then pick what works for your own body/lifestyle.

But injured backs REALLY need to be looked after - you only have one of them and you need it to last for a whole lifetime. I have a bit of back trouble occasionally and have found that if i rest it completely for two days, then do light stretches for two days, followed by light exercise then build up to back strengthening excercise I can limit the amount of downtime and pain involved.

You've accomplished a lot already by loosing 88 lbs. Sounds like maybe also you don't have confidence in your doctor, maybe you should look for second opinion. I have knee problems and my doctor recommends swimming and cycling but I like step/dance aerobics so I modify some and continue on my way.

First, how much do you weigh, perhaps you're not getting enough calories & that's slowing your metabolism. But no matter how much you weigh, you definitely shouldn't go lower than 1200. On the hypothyroidism...if your TSH levels are in a good range, then it shouldn't be an issue. That said, a LOT of labs & doctors are using outdated normal ranges. The practicing board certified endocrinologist expert who wrote, "Thyroid for Dummies," recommends 0.5-2.5. If you're not in that range, then I'd talk to your doctor about upping your dose. Remember, the higher your TSH is, the more medicine your body needs, because it's a sign the body is trying to produce it on its own.

On the back, I used to have trouble until I started doing some VERY easy (they seem more like stretching) exercises developed by physical therapist McKenzie. Most physical therapists are actually switching over to his methods, around the world, because of the great results they get. I joked w/my physical therapist that she was working herself out of a job. Here's the book link, but you don't have to read it all, just go straight to the back exercises section.

http://www.amazon.com/Steps-Pain-Free-Life-Rapidly-Relieve/dp/0452282772/

Also, weights, if done correctly should help ease back pain. If you're sore the next day, that's ok, but being sore 2 days later means you're going too hard. Increase your weights and/or reps very gradually. For weight training, if you're aren't sure about your form, I'd recommend "Body for Life."

http://www.amazon.com/Body-Life-Mental-Physical-Strength/dp/0060193395/

Definitely avoid that doctor in the future.

Strength training is so great for us at any age, but I agree, your back is your first priority.