Your lo sounds a little like mine a few weeks ago at five months. I also exclusively pumped, we had no routine whatsoever, dd was going to bed at 10/11pm at night and I couldn't get a routine in place.
I got a tip from mn about tracking a few days on paper to see if there was anything routiney already present. I split the day into 15 minute chunks, and wrote down what dd was doing at each point. I realised she was having a nap about 2.5 hours after she woke.
What I also noticed is that her routine naturally changed after we started solids at 6 months.
Now we have, very roughly...
7am-ish wake & first bottle.
9am breakfast.
10-11am-ish nap for an hour-ish.
12-1pm-ish nap for an hour-ish.
2pm lunch.
3-4-ish nap for an hour or two.
6pm dinner.
7pm up to bed.
8-9pm sleep.
In between these hours, we might have an afternoon walk or trip outside, playing on the floor, and I just feed dd a bottle of bm or formula when she wants one (I tend to do bottles of bm at night as it lasts longer outside of the fridge).
She still wakes a few times a night and has a tiny bit of milk.
Hope this helps. 