Hi there,
my lo is also 3.5mths and she used to have 6 feeds a day until yesterday when I swapped her to 5 feeds.
She used to feed 7, 10, 1, 4, 7, & 10pm (basically 3 hourly)
Now I am trying 7, 10.30, 2, 5.30, & 9.30pm (now 3.5 hourly)
To ensure she got enough to eat during the day, I was very patient with her feeding and encouraged her to drink as much as possible from both sides ....... and prayed that she didn't wake up hungry at night!
Well, last night she slept through till 5.30am and when she woke, I just gave her the dummy and she slept again till 7am. So I hope to continue this with success!
Hope this helps with your situation and good luck!