a baby... will usually get tired/sleepy, after 2 hours of "awake" time.
for this age, even a bath is an 'activity.'
Also, they get over-tired and over-stimulated easily at this age.
Then they get fussy... because they are already over-tired.
Over-tired babies/children do NOT sleep well, nor fall asleep well and have a harder time sleeping well.
For the 1st year, my kids napped 3 times a day. At that age.
Your baby is tired. Needs to nap.
If not, it makes it worse.
My son as a baby, had that late afternoon nap at that age... it was fine. He needed it. If you make them not nap... it makes it worse.
If they need to nap, they need to nap.