How to stay focused whilst studying?

What personally works for me is using Pomodoro method videos (check out Peaceful Ambience on YouTube for an example). This is either working for 25 mins with a 5 min break, or (the one I prefer) working for 50 minutes with a 10 minute break. If that seems intimidating then start with 25:5 videos.

During the time, make sure the space you're working in is set up for study. Put your phone on silent and somewhere else, and associate the sounds from the video with a place of work, such as a library. It helps me to almost 'gamify' study. There are also study apps you can get from your phone which will start a timer, and that app has to stay active for it to work. So that could be a solution if you find yourself reaching for your phone.

I think your main challenge though will be to address why it is you're procrastinating in the first place. Are you not enjoying the work, and if not is there a way you can approach it in a more engaging way? If it seems like a daunting task (if you're telling yourself you'd have to sit down and do a massive amount of work at once), then break it down into manageable chunks, and/or set a timer for 5 minutes. You'll manage that no problem, which will be a motivation boost and you can begin extending the duration of your distraction-free study sessions.

Personally speaking, a rewards system doesn't work for me, because then I'm just focused on the reward and not the study itself. That can sometimes cause me to bypass the study altogether, get the 'reward' and then I just feel bad and I'm no further along in my studies! I think focusing on making the most of the study so you enjoy it, whether through using nice stationery, having a nice chilled out video in the background, lighting a candle, etc. is more effective, at least for me. I hope this helps.

My problem is with pomodoro sometimes I'll be in a flow and then once the timer hits I stop working and my flow is gone

Ah I can see how that could be annoying. I try and plan my breaks to do something that gives my brain a 'break', but is still productive (so I still feel in my flow, if that makes sense!). E.g. make a cup of tea or some other drink, put my laundry on, feed the birds, put recycling out, bring some firewood in, do the dishes, etcetera.

That's why I do prefer the 50:10 though, because 5 minutes just isn't enough time for me to do most of those things!

So do u like set a timer for 50mins? I'm personally thinking I revise one lesson in a topic then take a five minute break then another lesson and a 5 min break etc until I finish the topic wdyt?