Nightfall is a natural phenomenon. Many a time frequent night fall leads to a certain type of weakness but it's again natural. so, do not worry.
excessive or everyday waste of Shukra dhatu is not good. so try to find ways out to engage your sense in meditation, bhakti, and good friends. At night in particular, after sunset, avoid talks about sex and avoid watching and hearing sex-arousing videos or conversations.
Health Tips
drink more water, engage your mind during day in bhakti and good friends