4.5 lbs is "about" the size of a 34wker. I have scans every week but I never find out any info until my 3D scans, which are once a month. My last 3D scan was Oct. 9th and at that time, my LO was 3lbs 14 oz. So that was 5 days ago if that helps any.
Hope your son gets better soon and fast!!