Nursing

Angelique
I'm very upset with myself, I feel as though I've let my daughter down. During my pregnancy I promised myself I would exclusively nurse my daughter until she was at the very least 1 year old.
But I felt it was very constricting, because my S.O is very protective, and didn't want me to nurse in public. So I was only able to nurse her in our bedroom with the doors shut.
Being a stay at home mom who also takes care of not only my daughter but my 2 step children it was difficult to juggle everything and I ended up giving in and gave my daughter formula. Then I gave it to her again, and again.
Now if I try to nurse she struggles to latch, and if by some miracle I do get her to latch, she will only nurse for about 3.5 minutes then she will begin to wiggle her body around and unlatch herself. If I try to relatch her she gets frustrated and crys until I give her a bottle. 
What do I do?