Being exhausted by 1 PM, specifically in a social sense
Problem: As a new intern, you're doing much more talking and listening than you usually do. You're asking questions, listening intently, observing how things are done, collaborating with teammates, and discussing plans.
But all that focus takes a lot of energy! So it's normal to find that your social stamina runs out by lunchtime. This can manifest as an aversion to talking to people any further, loss of verbal ability, difficulty in parsing spoken words, desire to move away from people, etc.
Solution: Take a break, find a dark, quiet place, and sit in for a while.
In terms of prevention, try exerting less effort as you socialize. For example, if you find it easier to look at a wall, table, or notebook while listening to someone (rather than carefully watching their eyes), do that instead.
In a WFH setting: try turning off your video in meetings to save yourself the work of unconsciously "acting" for the camera.
As your internship continues, you can expect your social stamina to improve to the point where you can make it through the whole day without hitting the wall.