3 week old major trapped gas and constipation

Hi everyone, I have a 3 week old who has major trapped gas and constipation. He is nursed and bottle fed breast milk and until 3-4 days ago he was pooping great, at least 6-7 times a day We have tried everything, belly massage, warm baths, Mylicon drops for gas, bicycles with legs and then knees to chest and it has helped a little but he is in so much pain… Any advice on what else we can try?!?