It's possible to have a completely supressed TSH and still have hypo
symptoms (be hypo).  My TSH is 0.1, but my Free T3, which is considered by
more progressive docs to be a better guage of actual thyroid hormone
activity in the body was still very low - i.e. my TSH was in the very hyper
range, but I was still hypo.

I'm very concerned about the fact that you are on 700 calories a day.  You
are not helping yourself this way.  You are shutting down your metabolism
even further and your body is burning it's own muscle to keep those 30
minute walks going.  I know it's scary, but you really need to add calories.
Have you checked out one of the lowcarb plans?  They have worked great for
many of us.  IMO, the best plan out there is "The Schwarzbein Principle",
developed by Dr. Diana Schwarzbein for her diabetic patients.  It may take
you a while to heal your metabolism if you've been doing this low cal thing
for a while.  Your body is almost definitely in starvation mode at this
point, conserving every little bit of food you put in and slowing all your
body functions down to conserve energy.

Good luck:-)
Sara