Welcome! You've come to the right place.
Lantus is a long-acting insulin designed to act as a basal to help maintain your blood sugar levels; however, it really shouldn't be thought of as a way to drive blood sugar down. That said, without a good base of background insulin, blood sugar would go up. With you on a basal-only insulin, the idea would be for other factors - diet, exercise and the insulin your pancreas produces in response to food - need to be managed to maintain a healthy blood glucose level. Generally, any carbohydrates (sugar, starch) drive blood sugars up, though some protein also is converted to sugar as well.
I've never been on a basal insulin only regimen, but I am certain others here have. As @David_dns suggests, you likely also need a rapid acting insulin to help manage meals -- and may need to see an endocrinologist.. I did take Lantus for a while, but did not have that 'foggy' feeling you seem to have from it. Not sure what that is.