Was wanting opinions from Nurses, Doc’s and other healthcare workers what could this illness be?

My father is a 61 yr old male who recently started to not feel well he had just been feeling "crappy" as he put it. So he went to the doctor they told him he might be diabetic so they tested him made a diagnosis and put him on diabetes meds. He continues to feel crappy and his blood sugars are fine so doc checks his Thyroid and tells him he’s Hyperthyroid and he needs to see a specialist. Meanwhile my fathers symptoms get worse he now has, Itchiness all over his arms, Tired and Weakness all the time, Constipation with Diarrhea (alternating), Sleeplessness, Extreme sweating, coughing with nausea, and difficulty swallowing or unable to swallow at times, and also he’s lost 70lbs in the last 2 months unintentional. What could this be? And why couldn’t his GP doctor just give him some medicine for his over active thyroid. I have hypo thyroid and i never had to see a specialist they just gave my some synthetic hormones and sent me home. I am really worried about my dad and he’s getting sicker everyday plus the dumb specialist won’t call him back he missed their first call to set up an appointment because he was at work and they called his house when he called them back the receptionist was hateful and told him you don’t call us to make an appointment we call you. Its been 2 weeks now and my dad is sicker than ever and their supposed to call today to set up an appointment, what could be wrong with my dad?