Welcome to the forum!
Improving concentration firstly requires getting rid of any distractions, particularly while you're studying. Those include any devices you don't use for study like your phone, or any other objects/factors that might distract you while studying. This ensures your focus is on your studies, not on anything irrelevant/which may cause you to waste time.
Addressing this issue also has to do with how much time you’re allocating towards your studies at home as well as how well your study plan is organised. Essentially, handling your studies effectively implies breaking your tasks down into manageable parts, which assists in simplifying and shaping your study goals more effectively. Since you mentioned you're having problems concentrating, returning to learning as well as being tired, you need to ensure you're regularly having breaks because the brain normally reaches a point where it is no longer able to handle/process information the way it's intended to, leading to lack of concentration, distraction and fatigue. Overwhelming pressure could be a cause for what you're currently experiencing and breaks are a good way of solving this problem.
I hope this helps!