LouandAlf,
what you are describing is actually meant to happen

it means your body has worked out what your LO needs, and is making the perfect amount, not too much and not too little! This is the age when they get more efficient eaters - a blessed relief to many who were having to spend an hour per feed at the beginning, but also distraction and impatience can set in.
You may find speeding up your letdown would help - a warm compress and/ or a bit of gentle breast massage before trying to squeeze out a bit to get things going, followed by breast compressions (see FAQs for how) to keep the milk stream stronger for longer. Moving into a quiet room away from distractions.
You're expressing a good amount - I never got more than 50mls even though I (usually) had plenty of milk. Remember, if you're getting that out with a pump your LO is getting way more - he's much more efficient.
Your nights are good which is another indication that he's not hungry - a hungry baby will not contentedly wait for breakfast!
Holding off on solids up to 6 months has a lot of long term health benefits - you can read more about it here:
https://babywhispererforums.com/index.php?topic=68263.0 at 4 months you wouldn't really be getting so many more calories into him from solids anyhow - squeezing in more milk would be much more beneficial, but it really doesn't sound like you've got anything to worry about!