Numbness in thumb and index finger?

If you have numbness beginning in fingers or toes, and you're diabetic, there's a strong possibility you're beginning to suffer from diabetic neuropathy (see links). This is very bad, since it means that your high blood sugar levels are beginning to cause permanent and progressive damage to your body. You can easily lose hands or feet within the next decades from this beginning.

Eyes and kidneys are at risk too.

Your best way to avoid these problems in future is to get much stricter with your daily blood sugar control. Work your way down, combining food and insulin changes, until your blood sugar is below 120 when fasting, and below 140 even right after meals. Test yourself before, 1 hour after, and 2 hours after meals and look up lower GI foods and short-acting insulins to avoid large blood sugar spikes or long-lasting high periods.

If you're not currently taking insulin, your diet control and medication are not adequate. You'll need to begin testing your own blood sugar frequently at home (meters are cheap), and learning to change your food choices and medication doses to meet the targets above. If that doesn't work, consult your doctor about starting insulin.

Also, there is increasing evidence that methylcobalamin (a special form of B-12 available widely) can help address and even reverse diabetic neuropathy, but its effects are limited if your blood glucose remains high.

The attached links will help with your research on neuropathy and blood sugar control.