Hello! Anything else changed in the past 6 weeks? I'm not entirely sure about the food but if that IS the culprit, the best place to start with that would be the doctor. Have you attempted going just bottles for a while to see if it gets better?
As far as looking at your routine, you may also be looking at a case of overtiredness. At 7 months you should be looking at 3-5 hours of napping during the day. If he has always done short naps and has been happy through all of his A times, then you're right and you could have a serial short napper. If he gets whiny/cranky during his A times you probably should start working on those and see if the naps don't improve.
At 7mos, he can most likely have a longer A time in the morning. A times can be 2.5 to 2.75 hrs in length...try pushing your A time in the morning back gradually - 5 mins every couple of days until you have him up until 10:30 or 10:45. Often this lengthens the first nap, and the rest of the day starts to settle into place.
That's where I'd start, anyway.
Let's go from here and come back if you have anymore questions.
Welcome!