Just because your thyroid labs are in the normal range, doesn't mean they are good for you... In the June 5 labs, your FT4 was actually above range, and so your thyroid was over producing, at that time, even though your FT3 was only at 51% of range. In the June 21 labs, your FT3 was at 3.9, which is 92% of its range; that's pretty high even though it's still in range and it took quite a jump in the 16 days between the 2 labs. Since FT3 is the hormone that's actually used by individual cells, it's easy to see why you might have hyper symptoms.
Since the endo said it appears that your thyroid is being attacked by your immune system, that means you have, either, Hashimoto's or Graves Disease... Your TPOab and TgAb are, both negative, and those are that antibodies for Hashimoto's, but that doesn't mean you don't have Hashimoto's, since some people are diagnosed with it, based on characteristics of their thyroid gland. I'm pretty much appalled that the endo didn't do further testing to find out exactly what's going on.
There's another antibody test that "should" have been done, called Thyroid Stimulating Immunoglobulin (TSI) that's used to confirm/rule out Graves Disease; that should have been done, so you'd know and if you don't have Graves Disease, you have Hashimoto's...
Some people with Hashimoto's have periods of hyper in the early stages that often alternate with hypo or even normal. This alternation can go on for years, before enough damage is done to the thyroid and one finally settles into permanent hypo. You should try to get your doctor to order the TSI test to confirm/rule out Graves Disease.
There are other beta blockers that can be used to control the rapid heart rates.
You try magnesium to help with the muscle aches/pains and you might try controlling symptoms with diet. There are some foods, called goitrogens that are supposed to interfere with thyroid hormone production... you could step up your intake and see if that helps. Those foods include the cruciferous vegetables such as cabbage, cauliflower, broccoli, brussels sprouts, kale, bok choy, radishes and others. Soy also disrupts thyroid hormone production and is not recommended for those that are hypo, so it might be an option.
I'm not a doctor and my first recommendation is to find a new doctor if your current one refuses to order further testing (the TSI test, specifically). You might also request that TPOab and TgAb be repeated in a few months, in case they just haven't ramped up yet...
Also, for future reference, Total T4, Total T3, FTI and T3 Uptake are considered obsolete and really don't give much information, so they're pretty much a waste of money...
What dosage of the Metoprolol are you on? Perhaps it's too high and you simply need a lower dose. Doctors don't always get it right the first time, even though they like to think they do.
However, it you don't feel comfortable with that doctor, don't stay there - get a different one.