Please Help!

My LO just turned 3 months yesterday. i have been Exclusively breast feeding and have been wanting to supplement with formula. After trying most of the brands I gave her. At first she tolerated the gentle ease ready to feed well but did not do well on the powder. I tried few other brands but nothing worked. Well I did not pump for one week and guess what she totally stopped taking a bottle after that. I tried most of the brands.  For the past two days I have noticed that she only nurses for 2 to 3 minutes at a time and that has affected my milk supply. I dont pump coz she does not take a bottle. I dont know what to do to make her full. It took me and hubby 35 mins to feed 1/2 ounce of formula. She was crying so much so we spoon fed her the formula. I dont know what to do it breaks out heart that she cries so much when we force feed her. Any tips?