A drastic change in behavior such as this requires that the both of you have a conversation.
It is not helpful to assume that she has been less affectionate of recent due to a big entry exam and personal stuff.
Indeed, the stress of all that, including the current quarantine situation can cause a change in behavior.
However, it is important that you don’t simply make that assumption.
You should have a conversation with her about what you have observed and try to get her to be open with you as far as what may be bothering her.
The sooner you know what the actual issue is, the sooner you will know whether she is willing to work on the issue with you.
If she is, then she is still interested and values the relationship.
If she is unwilling to work on it or does so lackadaisically, then she has most likely lost interest in the relationship and it will be only a matter of time before she ends it.