This is only AS bio but I got a U in the mock, B overall (in just a month, I didn't even work that hard)
You really can improve in 3 months, some exams are in 4 months time.
I too am struggling with motivation and laziness, my only advice would be to think about why you are doing it (uni, job, make yourself proud etc) Ik someone who wanted to be a paramedic and so their parent stuck a picture of an ambulance over the tv and near her desk. But anyway have some way of reminding yourself of your goals