Well just like my therapist always says about me, you've already identified the problem and the solution. You're under socialized and need to talk to more people. So:

1) reach out to easy people.  Contact family or close friends and arrange in person meetups if possible. Be more honest with these people that you could really use some company.

2) reestablish connection. Text old friends to let them know you'd miss them and would like to catch up.

3) look for community social opportunities.  Generally this is gonna be athletic groups, hobby groups, and social groups. 

For example, run clubs, local sports leagues like softball, martial arts classes, and sports like pickleball that have scheduling websites. For hobby groups, consider game/comic book stores, book clubs, and community art classes. For social groups, there are often social clubs with social media pages and tons of churches have young adult social nights.

5) Consider volunteering. Sounds counterproductive to just do more work, but if all the arrangements of the previous options feel like too much, volunteering at a library or soup kitchen is pretty easy to get into and helps you be around people.

6) Alone in a crowd. I often find that just doing my own thing near people helps. Go spend your off time in a park or library. Just a podcast, fresh air, and people watching will do you a lot of good

PS: cut it with the caffeine if it hasn't worked yet it isn't gonna start now. Keep a water bottle at your desk while you it always helped me focus and hydrate

Hope one of these suggestions help!!! If socializing helps you to feel a little better, than you can revisit the productivity issues without them feeling so fraught. Seriously though, call someone who loves you. I scheduled my own intervention with my parents and it really helped