I see that you're... aroused. That's completely normal, and it shouldn't be causing you any pain or discomfort. What might have happened is that something stimulated your body, making your penis become erect in response. It could be from what we talked about earlier, or even just thinking about someone or something that turns you on.
Is there anything else bothering you down there? If not, I can help you with this by teaching you how to manage an erection if it happens again in the future.