Hi,
How are you? The rash and itching from poison ivy usually get better gradually and go away completely in two to three weeks. Treatment should be continued at least this long because the rash can come back if medicines are stopped too soon. Take your medications as prescribed by your doctor and avoid exposure to the plant to prevent recurrences. If symptoms persists, it is best that you inform your doctor for proper management. Take care and do keep us posted.
It can take some time for your immune system to stop reacting to the toxin after exposure. You should notice it decreasing soon. If not, talk to your health care provider.