Lemons as with most citrus, do not need to be pollinated to produce fruit. They are parthenocarpic (self-fruitful). Don't worry about missing stigmas :-) And, hard to say why your tree is bearing less fruit this year, it can be due to several different things, such as how long you left mature fruit on the tree (which can force a tree to alternate bear), fertilizing and watering, pest pressure, cold/freezing temps (tree would be in recovery), etc.

Patty S.