I agree with all of you. Keep in mind that BF can take up to 8 weeks to be established. At 5 weeks with my ds, he was having a growthspurt, but he was extremely fussy as well. Just feed when your LO is hungry for now. At 3 months, our ds started to get fussy with his last feed, so we introduced a bottle of formula at night at 4 months and it helps a bit, but not always. Of course, we only give him 4 oz max, so that is part of the reason!
I would wait a few more weeks before introducing a bottle everynight, and when you do start, try to use expressed BM.