I sleep better when I'm riding a bike regularly, but I have other issues as well that affect my sleep. Biking is exercise and it should improve your sleep quality. But in the beginning it may make you more exhausted to point of discomfort. Although, normally, physical exhaustion should lead to better sleep. But think of the people who work physically all day. You just should get used to the extra physical activity eventually and become stronger. I get tired towards the end of the week whether I ride or not. My work burns me out mentally and low mental energy leads to physical weakness.