D.M.
Y.,
Ditto Susan's advice...
My son was comob fed breast/bottle until he was almost a year old. He went through phases where he just wanted a bottle, and really I just had to give in. But, mostly it was during times when the bottle was just more suited to his needs. Like Susan said during times of teething and sometimes when he was sick, too. By the time he was 1 yr. I had to give in and let him go with the bottle and take care of my health issues.
If you are really concerned you might enlist the help of a lactation consultant...they can give you tips and help that apply to your situation. I found mine through the hospital where my son was born...often a consultation is free and sometimes they will come to your house!
Good Luck!