My daughter is not a big eater. She is 2.5, and she still isn't, but her behavior at 6 months sounds a bit like this. She fought tooth and nail to keep that food away from her. She was over a year before she at any sort of solid food regularly, she never took a bottle, etc. etc. Things that i understand:
1. the iron in breast milk is actually well absorbed, so, you probably don't have to worry. at 9 months my doctor had me test my daughter's iron, and it was fine. We did, at that time, start her on poly-v-sol vitamins as a precaution, though.
2. Seems like some kids just don't need to eat that early, especially if they are getting good breast milk. my son is also not a big eater, at 6 months. (he is barely eating anything yet). They are both, however, astoundingly healthy, and have always grown well. They tend to be on time or ahead of developmental milestones, and are rarely sick. I have since heard of many many folks whose babies were 'late' eaters, with no ill effects.
3. At around 10/11 months we had our daughter evaluated by a specialist to make sure there was nothing physiological wrong with her that we should be addressing. She was diagnosed with a mild sensory-integration disorder, but nothing physiologically wrong. The sensory issues just mean that she is pretty sensitive to new feelings and smells and tastes. (She is cautious by nature, so this fits the rest of her personality.) The prescription was (and still is) to try to desensitize her by exposing her to new textures and flavors in a very stress free environment. The doctor gave us a 'nuk brush' to use to help desensitize her mouth. We were instructed to let her spend lots of time playing with baby food with her hands, and to let her experiment with feeding herself - mess and how much she consumed were to be ignored.
4. As much as i can read about eating issues in kids suggests that the job is Parents supply the food, Kids are in charge of eating it. Once you make the appropriate food available, your job is done. Only your kid can eat or not eat. (Book recommendation - How to get your kid to eat, but not too much. Advise repeated in many other readings and doctor.)
5. I think some of our on-going problems with our daughter are because we got so anxious to get her to eat something, anything, medicine included, that it became a high stress power struggle that we haven't been able to correct.
6. If i had to do it again (and, lucky me, i do - we are doing this with our son), i'd start by not stressing. Until the time when the doctor feels like growth or development are being delayed, totally ignore how much your kid is eating. If grown and development are being delayed, consult a specialist about what steps to take.
Secondly, i'd provide more play time with food, the nuk brush, and utensiles without worrying at all about whether the food was consumed.
Thirdly, i'd back off whenever tensions get high, or the kid appears done. At six months - if feeding isn't fun for the kid, its not that important.
Fourthly, i do place food in my son's mouth even if he doesn't lunge for it, because i need him to figure out that it is food and tastes good, but i don't force the issues.
(And, fifthly, for medicine, we really did need to hold our daughter and squirt something deep into the back of her mouth. I do this with my son and try to get it over with quickly. It sucks. the nurse at my doctor's office, however, seems to be better and sneaking in just the tip of the syringe and putting it in a tiny drop at a time.)
Good luck, and, really, hang in there.