Poor mental health. This further.

Hi. Being in the same age group, I can understand how you feel. With great power comes great responsibility and stress as well. It is okay if you feel a little stressed out or not able to keep up with the pace of life. Your stress level would increase if you try too hard to do everything at once or try to keep up with everything that's happening around you. Too much pressure on self could be another reason for stress and low concentration. Also, when we have responsibilities, we tend to ignore our needs, wants and wishes. We don't do things that we liked to do earlier, leading to more stress. These activities help us to relieve some of the stress. Take small steps and keep your schedule light. I would suggest you to read up on Mindfulness and keep your inner child happy by doing things that you liked for example, cooking, going out for a walk and so on.

I would suggest you to see a counselor and work on scheduling and getting back your focus.