I have a 44lb 3foot 10inch 5 year old son who I think is small. Is this a good hight weight combo?

Yes. If you plot his height and weight on a chart you will find he is in the 50th percentile in weight and maybe 90th percentile in height. There is nothing about that which raises any red flags. Hopefully the pediatrician has been plotting his growth and will let you see how he how he has been progressing and i would check with them.