I have 3 children, I tried breast feeding my 1st and due to him having quite sever reflux, was unable to feed him more than about 4 weeks.
I was more determined with my 2nd, we went through hell, breast refusal and bottle refusal, in the end, I fed her for 12 months then weaned straight to a cup.
I wanted to do the same with my 3rd, however in the back of my mind wondered if i would be able to, as i was returning to full time work when she was 3 weeks old. She came to work with me until she was 12 weeks, then had to stay at home with grandma. I continued breast feeding when i wasn't at work, and because i couldn't express enough to give her 2 -3 bottles / day, she was given formula while i was at work.
She is now 19 weeks old, at 16 weeks, she had to go to full bottle because my milk started drying up, she just wasn't getting enough from me.
As much as i enjoyed breast feeding, i can see many reasons why some women don't.
It's great of you to encourage something as healthy and natural as breast feeding, especially since you enjoyed it so much, but don't go to the point of making someone feel guilty if they don't, there may be underlying reasons why.
Just for the record, my baby that was breastfed for the longer period of 12 months has had more medical problems than my others, and also suffers with terrible food allergies. So breast feeding doesn't necessarily make them stronger, or less suseptible to illnesses.
Mel, mum of Joshua 8, Maddison 5, Hailey 5 mths