Always variations in FBS, PPBS, and

I am 32 male, I was diagnosed with diabetes 2.5 years back. At that time my hba1c was 8.1. fbs was 232. After that I avoided white sugar mostly, not following physical activities fully, but doing. I am a IT professional. Somewhat stressful sometimes only. After my first hba1c, taking it regularly, my last three hba1c was 6.2,5.9,5.7..but here the case is FBS most of the times 140, PPBS is 250 to 300. Yesterday my RBS was 280, hba1c is 5.9, why this is happening. I am also having NAFLD grade 1, and GERD with hiatus hernia and anxiety. Echo and ECG is normal. In LFT test sgpt is 84.KFT is normal, thyroid is normal. Doctor told life style change is enough as of now. Taking medicines for GERD with LPR, like DSR, nexium 40, becalm. Inderal f sometimes. With GERD symptoms, I am feeling more tired. What are the reasons for this reading variations ?