I am sorry to hear that your baby brother's ear was hurting him and he was taken to a physician, and given antibiotics, and now he has a fairly high fever of 103 F and you are worried about what to do. First off I am reassured that your baby brother has such a caring older sibling. I am happy to give you some of my initial thoughts about what might be going on, and what to do about it, but ultimately I am going to defer to the judgement of your mother, and the physician that she has seen already. There are many different reasons for a young child to develop a high fever. Being that your little brother had an earache that preceded this fever, it is completely reasonable that he could have an ear infection
that could be causing the fever. However there is a phenomenon called referred pain, where the body sense pain in one location when there is actually going on in another location altogether. This happens with the throat and ear. So another thing to consider is that your brother may have a sore throat
(like strep throat) and be sensing pain in the ear. Either of these situations could potentially give a high fever. For a fever of 103, I would give him tylenol or ibuprofen to lower the temperature, and if the fever decreases with the treatment, I would call the doctors
office first thing in the morning and let them know because they may want to see him again. If he becomes lethargic (excessively sleepy) and seems like he is sicker and not responding, or if he isn't taking anything by mouth (like liquids), then it may be a good idea to go to the ED. Best of luck.