This is normal and something every guy goes through. Two effective ways to start getting back out there and regaining confidence are small wins and great friends. Dr. Geoffrey Miller begins this Q&A episode talking about making small steps to be more outgoing, with women and with friends. Tucker Max brings up social relationships and how a great thing to do is engage with good friends in positive, uplifting ways. Many problems start with not having friends. 
This is something that most dating advice never focuses on. Social relationships are so important to mental health, confidence, and even hormones like testosterone. As humans we need strong relationships, especially during tough times. And as men most of our friendships are made in structured social groups with a common set of goals and values. Sports clubs, the military, and startup culture are good examples but there are 100s. Start with finding those groups. You can listen to the Jack Donovan (The Way of Men) episode for a more in depth talk on this.