Not gaining the recommended weight during pregnancy

I’m 23, 5’6 and before I was pregnant I was 61kg. I’m currently 33+4 and I have just weighed myself and I am only 69.5kg, 4.7kg less than what I am meant to be. I have been having scheduled scans since I was 28 weeks due to baby being a slow grower (I’m healthy and everything is healthy with him also) I just wondered, is my baby growing slow because I’ve not gained the recommended weight, and are there any complications that can arise due to me not gaining the recommended weight?

My midwife hasn’t weighed me since I was in my second trimester, and when I see her in a couple of days I will ask to be weighed. Thanks!