My son at 3 mths jab already 8.45kg, also 150ml / 3hrs (sometimes cannot finish). The nurse at polyclinic told me, not to worry too much of his weight gain, cuz it'll slow down when he learns to crawl. She also ask me to start solids at 6mths. So i dont think you should get too worried.
For your info, my friend's son at 2mths already 8.8kg. Now at 5.5 mths already 10 kg plus !