Missing last nap

[SHP129]

Hi, I have an 18 week old who naps anywhere from 30 mins to 2-2.5 hours. We've found our routine and it seems to be working just fine, however he has his 4th feeding of the day around 4/4:30pm and then stays up for 1 hr 45 mins to 2 hrs. He sometimes refuses or fights the next nap which then results to overtiredness or he will fall asleep and then won't wake up until the middle of the night (so he only gets 4 feedings in the day). My question is 1. Is it ok for him to have 4 feedings in the day? (He has plenty of wet and dirty diapers and seems to be gaining weight, but definitely gaining at a slower rate... He's also on the smaller side) and 2. Is it ok to wake baby to get in one more feeding for the night so he sleeps through the night?

We used to be on a 3 hr schedule where his last feed of the day was at 6pm and he'd go down for the night around 7:30pm and would wake up around 5-6am which was working so well. He was eat at the 3, 6, 9, 12, 3, and 6 o'clock times give or take but for me to stay on that schedule I would sometimes have to wake him (which I don't do anymore). So now he's kind of all over the place...

[creations]

Hi
Sorry I'm a a bit confused as to when his E times are.  If the 4ht E time is at 4.30 and he then stays awake to BT you would be feeding again before BT. It's usually the last thing before night sleep.
Otherwise if he's happy to sleep through the night without a feed this isn't a problem unless weight gain is so low that a medical professional has told you you must wake him to feed.
LOs don't tend to gain weight steadily the way we might expect, it's like they don't gain for a while and then suddenly have a growth spurt and have leaped up in weight in one go.  Also it is normal for some LOs to be smaller and some bigger.  The key is they follow their own centile line on the growth chart (you are not aiming to make a small baby into a big baby), it is within the normal range to cross one centile line on the chart but if 2 are crossed then this can indicate a problem.
My own DS was/is small.  He ate half the guidance amount and had me constantly worried about how much he ate.  However he did keep to his centile line so although some health care professionals were also concerned about the amount of milk he took when they weighed him they were sure he was fine.

[SHP129]

Here's his "schedule"

E- 6am (he wakes anywhere from 5-6am though. He's never screaming or crying much so I can hold off the first feeding to start the day off at 6am)
A- usually 1.5-1 hr 45 mins
S- 7:15am (because most of the time he wakes earlier than 6 so I count his awake time from the time he wakes up)

E- 9/9:30am
A- 1 hr 45 mins to 2 hrs
S- 10:45/11 to 12pm (give or take)

E- 12/12:30am
A- 1 hr 45 mins to 2 hrs
S- 1:45/2 to 3pm (give or take)

E- 3/3:30pm
A- 1 hr 45 mins to 2 hrs
S- usually napped around 5pm but now is fighting this... Which I can't seem to figure out how to avoid a super long awake time before bedtime

E- 6/6:30pm
Bedtime- 7/7:30 (asleep by 7:30/8)

Some new things he's been doing is:
--taking one nap that's about 2.5/3 hours which then throws off the above schedule
--waking up around midnight and crying for 45 mins even when held or rocked (I did go back to work this week so maybe this is why...)?
--the early morning waking (5/5:30am)
--90% of the time he wakes a lot earlier than his E time so then it throws off the schedule again because he's awake for longer...

Help please!

[creations]

Hi there
Sorry I haven't been able to reply sooner, I have a bad back.

It looks like your LO is ready to reduce the number of naps and increase A time.  Here's a couple of links which should help:
https://babywhispererforums.com/index.php?topic=84884.0
https://babywhispererforums.com/index.php?topic=246541.0

When increasing A times it's usually best to go up by about 15 mins every few days rather than adding 30 or 45 mins all in one go.  The longer A time would help to increase nap length and then the routine should hopefully settle down.
If LO finds it hard to transition between sleep cycles you can use W2S:
https://babywhispererforums.com/index.php?topic=223809.0
look at naps option 1 where you help before LO wakes rather than disturbing or waiting for him to wake.

The increased A time before the first nap should also help to discourage the earlier wake up time in the morning.

The night waking may be due to hunger, perhaps try a feed if he isn't resettling.  There are still growth spurts and LOs are still expected to feed at night at this age.

hope this helps a bit