Proof that it can happen!!
I have a friend who fell pregnant (by mistake unfortunately - she believed the 'can't fall pregnant while breastfeeding' story) when her baby was just 10 weeks old.
She breastfed her baby through her pregnancy, and weaned just before her baby was born (see her sisters story below for weaning reason).
Her sister also fell pregnant while breastfeeding her 1 year old. She continued to breastfeed the 1 year old after she had the new baby with no problems - on the breastfeeding side anyway.
The one problem she did have with feeding a toddler and a baby is that the toddler started getting jealous, and was hurting the baby because he didn't like it taking his dinner away from him. She was a member of nursing mums assoc, so she had a lot of support, advise and assistance, and they all came out of it ok, from memory she weaned the toddler onto a cup just after he turned 2.
For the record, i breastfed my 1st little girl until she was 1, and had to stop feeding this one when she was 16 weeks because my milk dried up (I went back to full time work at 3 weeks post partum - and starting formula supplement feeds when she was 8 weeks because my milk was starting to dwindle - and no amount of pumping was bringing it back - stress i think).
Good luck, and keep trying (i don't know how you find time to try though........re: topic, juggling work, family, domestic stuff ha ha ha)!!!
Make sure you let us know when you fall.
Mel, mum of Joshua 8, Maddison 5, Hailey 5 mths