Feeling like a failure

Molly
HI ladies. I cannot help like feeling like a failure. My LO is 11 weeks old. At her 2 month appointment she was in the 5% for weight (down from 41%). Doctor and I discussed our options and we decided I would feed more often and at night (since she was doing 8-10 hour stretchs) also burping more often as she has been spitting up a ton. 2 weeks later (today) we had a checkup, she gained about half of what she should and is now in the 4% after all my efforts, waking up at night feeding every 2 hours, Im exhausted. She only takes 30 minute naps so i cant rest during the day. We decided since I had tons of pumped milk from all those nights she slept we would supplement after feedings if I felt she spit up more than an ounce. Today when I got home I fed her and she spit up a lot. My husband gave her a bottle and she guzzled 6 Oz. And didn't spit any up! I was astonished. I started crying and felt like such a failure. How could she eat that much!? I feel like I've been starving her and completely failing as a mom. I feel so much guilt and anxiety. I feel like I don't know what the hell I'm doing and she's suffering from my lack of motherly instinct. The extra milk will work for now but what happens when that runs out? I'm thinking pumping but when do I have time? Please send words of encouragement or your stories to help me through this. TIA