The trouble with knowing myself

So, I need a new perspective on this. Someone close to me recently got a very painful but, not life threatening injury. They were prescribed a medication that helped in the healing process. Now, they could go back and get a refill as they are almost out of the meds but, they just asked me to go get some of this medication from another family member, along with some painkillers that might be helpful for me as I have a chronic pain condition. Was it selfish or mean of me to say no? I have two kids and as their sole caretaker if I went to jail for having a bunch of pills on me who would take care of them. I have no family or friends who could do me that big of a favor, and I wouldn't even deserve help if I did something so stupid but, this person is using every tactic in the book to make me feel like I'm an absolute selfish pos. Was I wrong? Am I selfish? Thanks for any replies!