If you have a teacher who is a good role model they will pay close attention to posture. Practising for hours with bad technique is the biggest cause of hand injury going!
When you learn anything new, take it slowly. Think about hand positions, posture, breathing, correct fingering. Avoid stumbling through at a pace you find diffcult. Playing too fast causes stress and strain and makes mistakes permanent too!
Pain is nature's way of telling you to STOP. Whether that is an extra half an hour's scale practice at breakneck speed or sticking your hand into boiling water, the message from your nerves is STOP. Listen to that message!
Playing with cold hands is as bad as trying to run a sprint without warming up. Something can and probably will snap eventually! Run your hands under warm water, massage your forearms with gentle thumb circles, do gentle slow exercises focusing on mobility and perfect hand position. After the "race" you need to wind down too. Same with practising. Relax....
Everyone learns at a different pace. Some musicians play faster than others, some focus on the personality of their music and focus on expression and tone. IT'S ALL GOOD! The number of notes per minute is not the sole indicator of skill. Be patient, be a survivor, take your time, work on it quietly, don't be drawn into showing off.
Don't be a slavedriver when it comes to practising. Let your hands recover. Walk around the room. Make a coffee. Read a book. Watch TV. Have a snack.....
Learning any skill takes time, planning and evaluation. Musicians develop fine motor skills over many years and over that time they also develop their listening and interpreting too. Be patient with yourself!