Mixed Feeding -bowel movements - 18 days old

[cheshirem2b]

My little girl is 18days old. She started losing weight on exclusive bf as my supply wasn't good enough for her but her bowels were regular at at least 1 if not 2 poos a day.
Due to the weight loss the feeding team at our hospital advised me to put her on a mixed feeding plan (2xformula then 1xbf) and I have to say she is slowly gaining weight and appears more settled after every feed now that she is getting enough.
However, we started mixed feeding on Friday. She had a poo on Friday night then nothing until Sunday lunch time. Then nothing until she did a massive explosive poo at around 11pm on Monday night and then nothing since.
I know that babies poo less with formula as it's harder to digest but does anyone have experience of a similar situation?
She isn't straining or in any discomfort. She has at least 6or 7 heavy wet nappies each day and is well hydrated.
Midwife is coming tomorrow so if we haven't seen any poo by then I'll ask her to check things out for me.
I've heard baby massage can help move things along - would anyone recommend this for her?