I'm sorry, your thyroxine dose doesn't make any sense. We usually talk about thyroid hormones in mcg, not mg. 12.5 mg would be a huge dose, and doubtful anybody would start on that high a dose. But 12.5 mcg is a rediculously small dose, and I can't imagine a doctor starting you on such a low dose, either - unless he was really, really ignorant about thyroid.
The normal protocol is to start on 50 mcg - unless you have heart disease - and retest after six weeks (it takes that long for the thyroxine to take full effect). Then increase by 25 mcg, and retest in another six weeks, and to continue that proceedure until all the symptoms are gone.
If you have been on 12.5 mcg thyroxine for 3 months, it's really not surprising that your TSH is 7.8. You need an increase in dose - preferably 25 mcg.
Thyroidinum is a homeopathic remedy, and has been mentioned on here before. And the general opinion is that it doesn't work. It will not do anything for your hypothyroidism. They only thing that can replace thyroid hormones is thyroid hormones.
Diogenes is a renowned scientist and researcher into all things thyroid.