You are correct that you could develop mastitis if milk collects in your breast.  There are probably services from lactation experts in your community that would be free or inexpensive.  See if there are any LaLeche League volunteers in your community.  This organization is dedicated to helping women have a successful nursing experience.  Call the office of the doctor who delivered the baby and ask for information about who can help you.  If you do run a fever or if your breast turns red, you will be past home remedies and will need to see the doctor.  In the meantime, keep up the massage and hot compresses.  I hope you soon see an improvement.