Excessive Weakness and fatigue. To do.

3 weeks back I had cold,flu,fever. Consulted with General physician she prescribed anti flu medicine for 5 days and dolo 650. Recovered from cold but since that time I am having too much Weakness and tiredness whole day. When wake up in morning I feel like I didn't sleep whole night feels not to get up from bed even though I sleep around 10 hrs everyday and proper sleep. Then I consulted one General physician at Apollo clinic 2 weeks back. He suggested to do one x ray to chek sinus. After checking x ray he told I have sinus and prescribed one antibiotic for 7 days , M Lc for 20 days and Azeflo nasal spray for 2 weeks + dolo 650. And also had vit b12 test done it was 139. He also advised M cob Od capsule for 3 months daily and b12 injection (optineuron) for 8 weeks. But now still no improvement in weakness. Still having same too much Weakness and fatigue. Kindly suggest what to do.