Q: Whenever I play for periods of time my finger starts to hurt and almost bleed. What should I do?
A: How long have you been playing? Are you a beginner or advanced player?
If you are a beginner, then your fingers will need to develop calluses (a toughening of the skin) through regular playing. I would recommend playing your instrument just to the point when you begin to notice some soreness in the fingers - then STOP. Continue again the next day again just until you feel your fingertips hurt. After a period of one to two weeks, the fingertips will begin to callus in response to the pressure (this is the body's innate response to stress on the fingertips).
If you have been playing for a long period of time and are devloping these hand symptoms, you should consider how much pressure you're placing on the strings. Use this simple test - push down on the strings at your body's strongest possible force. Register this pressure in your brain and give it a 100% rating. Now barely touch the strings with your fingers and give this a 0% rating. You should be able to produce a tone with about 30% of your maximum pressure. (This varies depending upon string gauge and action). Take a serious look at how much pressure you are using to play.