C.,
No worries. Until you baby is AT LEAST a year old, your milk has absolutely everything he needs for his nutrition. Some babies don't eat well even past that age, and they do just fine! Babies that are prone to allergies will often avoid foods until they are older. Their body is protecting them from a substance that can harm them.
Often babies simply don't like baby food from a jar. If he is 8 months old, you can start him on some soft table foods. Steamed veggies and fruits, or soft fruits, small pieces of pasta, and soft-cooked meat are great for early foods. Meat is especially important at this age, because it provides a great source of iron that is absorbable by baby's body, unlike many "iron-fortified" foods like cereals. Neither of my daughters liked baby food. The first ate it for a while, then went back to the breast until she was old enough for table foods. With my second, we bypassed baby food altogether and went straight to table foods. You can also buy a babyfood mill for very little money and grind up whatever the rest of you are having for dinner. By doing this, you know what is in your baby's food, and he gets the taste and nutritional benefit of fresh foods. This is the one we have: http://www.amazon.com/Baby-Food-Mill-1-unit/dp/B00016X0GY
My youngest is 14 months, and she still goes through phases where she prefers breastmilk to food. If you are physically uncomfortable from constant nursing, you can try offering him a cup and/or snack when he asks to nurse. You can also try distracting him with some playtime or a book. If he is insistent about nursing, he probably needs to, so just go for it. Make sure he is positioned well at the breast, and use lanolin between nursing if you are getting sore. He will grow into food, in his own time.
Best of luck,
S.