10 week old not eating

My 10 weeks old has recently lost his apatite. Previously he would take 4 oz every 2 hours and now making him take 3 oz is a big struggle. Some days ago he slept from 9 pm to 7 am and didnt wake up for feed. He was very cranky the next morning. Now i wake him up by changing nappy after 3to4 hours at night to feed him. So that he eats. He has dropped from 12 percentle at birth to 1 at 6 week checkup. I was EBF at that time and didnt know he was toungue tie. After that i started pumping n giving him botttle. Im worried now cuz i want him to gain wieght and he doesn't want to eat.