My ds is a daytime catnapper and always has been (though he does sleep great at night) and never has the 2/3 hour nap suggested when I read routines!
He's also 5 months and weaning 
Will your ds fall asleep in the car/pram? Mine will so my day looks like this;
Up at 6.30am (dh gets up then mon-fri for work so ds is sort of set to wake around this time)
7am - bottle (7oz)
7.45am - wash/dress
8am - breakfast usually 2 heaped teaspoons of baby breakfast.
Then he plays on his play mat while I dry my hair/eat.
8.30am/8.45am he has a milk top up usually and then has a snooze on me for about 30 mins. Otherwise we go out in the car to a group/the next village so we can walk and he naps then. I live rurally on a narrow lane so can't walk from my front door.
11am (ish) we head home from group or whatever and so he may have 10 minutes in the car (Or longer if he's particularly tired and I drive home the long way!)
12pm lunch and milk.
We then play at home for a while.
3pm milk and then I sometimes nip to the shops so he may snooze for 30mins then. I deliberately don't buy everything in one big shop 
4/4.15pm he has his tea and sometimes more milk (he's a hungry boy!!)
we then play or he sits in the bouncer/highchair while I tidy the kitchen.
6pm bath and into sleepsuit then milk, into sleeping bag and bed for 6.45pm.
DH gets home during bath so he always does bed while I cook dinner.
May I ask does your ds feed in the night each time he wakes? I'm guessing not?
It sounds like he could be over tired so maybe trying to 'force' a couple of naps in the day as I do will help at night?