Stress can impact our ability to enjoy masturbation/sex. It sounds like you might be experiencing arousal discordance. "Arousal discordance means that physiological (in this case, bodily) and mental arousal don’t match up at the same time. This can go in either direction: you can want sex mentally but your body may not be ready, or your body might be raring to go even though you don’t actually want to have sex." - The Great Arousal Mismatch: When Bodies and Brains Don't Line Up
Check out this article it has a lot of good information on the topic!
Stress can make it hard for us to relax and even though we might be thinking "I want to have sex," your body might be getting signals that its not a good time for that. Stress can indicate to our bodies that we are not in a situation safe enough to be relaxed in putting us in "fight or flight or freeze mode". This is an instinct animals have too! But for humans, our stress levels don't always match up with the actual risk so it can be confusing for us when our bodies respond that way. All of this is to say, there's a very good chance finals stress might be making it hard for your body to relax. The good news is finals are temporary! Also there are things you can try to help your body along. Lube is your friend!
On the off chance that this is not what you are experiencing, one thing to test out is maybe trying to find different ways to pleasure yourself. " If you're trying to do what you think
should feel good, instead of experimenting a lot to find out what you yourself actually like, that can keep you from finding your own grooves. Try and keep a balance of copying what you have seen or heard about with just trying things that come from your own head or what your body is responding to." - Going Solo: The Basics of Masturbation
If fingering isn't feeling good right now, you can try other forms of pleasure stimulation. From vibrators to pillows, there's a lot of things you can safely explore right now. The article I just took a quote from above has a lot of different ideas of kinds of masturbation you can explore. Check it out!
If neither of these things are resonating with you feel free to follow up and we can talk more about what you're experiencing. Also, feel free to ask any questions.
Hope this helps.