Why is feeding so hard! :(?

I'm a new 19 year old mom to a beautiful baby girl she is 3 months old. I have fed her this whole time but everyday has been so hard for me to feed. She won't latch on all the time, she likes to look around everywhere & it takes forever until she does latch on. She eats only 15 min max on one only. I've been pumping almost all her feedings she eats about 5 oz but sometimes I run out of milk and I feel so guilty to give up and give her formula because I stay home with her all day and I feel that I should feed. It makes me really sad that feeding is so hard for me. It also really stresses me out to the point where I'm crying almost everyday. I wanted it to work so bad but it's so hard. It makes me very,very tired to be making bottle after bottle after bottle especially when she's crying of hunger and won't latch on. Please help me i thought it would be so easy and a nice bonding moment but it's not it's more like a struggle. I'm really starting to think if I should switch to formula. Can I breastfeed & also give her formula?