Sugar levels fluctuating a lot.

My father is 64 years of age having diabetes from last 20 years. Taking medicines of course. His doc has changed his medicine from last 1.5 month and after which he feels weak , sluggish and dizzy sometimes. His sugar levels are fluctuating a lot. Thus effecting bp too. His random and general sugar levels are in the range of 200 to 250. Off late he has had episodes of shivering, ghabraahat and dip in bp which has never happened before. During the time of ghabraahat his sugar levels were 200 something but bp didn't show on the monitor. Has happened a couple of times ...When he is lil stable and reaches to a doc..His bp comes as normal. He feels weak and numb during that ghabraahat phase. What could be the reason of all this? Is it the effect of some medicines? These are the medicines he is taking.. Telsartan H for bp Tenlimac M 1000 twice a day for sugar POP DSR for gas Ecospirin Jubinerv Pregator Plz advice.