Shakespeare is saying that his love is like a fever that stays forever (doesn't go away), and craves what harms the disease.It feeds on what makes or keep the illness there. The fever cant and isn't getting better because it craves what makes the illness worse. Shakespeare compares his "love" to any illness. On line four he basically says his fever actually feeds on the thing that helps the illness, and he does it to fulfill the craving. On the lines, 5-7, shows that his "physician" is mad or ticked off at him and has abandoned him because Shakespeare doesn't follow his orders and or "prescriptions". He is thinking about his death. Lines 9-10 shows how he is now so sick, that there is no hope of a cure. His inability to reason or think correctly
