Everybody solves things differently. For me, I find that by writing everything down in my agenda, it helps me organize my thoughts and I'm able to visually see what assignment(s) are due soon.
Since your history exam is coming up, I would highly suggest you to study a bit each day. It's a bit of a stretch since May isn't even here yet, but it's better to start early.
Once again, although May isn't here yet, I would suggest working on whatever is due in that month. Believe me, doing it last minute is seriously so stressful and you'll regret it. (I'm saying this from experience.)
Just remember to give yourself little breaks and be sure to have enough sleep! It's fine if there will be times where you find yourself staying up the whole night just to get your work done. But, don't do it often as that is not good for your health.
Some tips for when you find yourself getting stressed out while working. I heard that tea, specifically Chamomile tea, helps reduce stress. Perhaps listening to music or taking a walk outside will help.
I hope my tips help you at least a bit.