Uncontrolled blood sugar levels. 2 year!

My father who is 67 year old was diagnosed with high sugar level like fasting 372 and post meal 419, cholesterol 5.9 and thyroid 9.41 so consulted doctor he gave medication such as zava met 60mg, trivoglitor forte 2, d3 kind 60k and thyrox 12.5 and strict diet. we followed it strictly then after 15 day his sugar level went very low like fasting 89 and post meal 69 for a couple of days then we again consulted the same doctor he advised to stop zava met 60mg, trivoglitor forte 2 and asked to monitor sugar leven it went fine for 1 week or so then again since 3 days it went up like fasting 124 and post meal 202 is the medication going in correct direction or should i change the doctor as he is getting weaker and weaker day by day some day he feels better some day he is not not taking any diabetic tablet as advised by the same doctor and following strict dieat he has heart precondition like he got 1 minor heart attack , so BP medicines are on going since 2 year