Is your baby on track?

My son is almost 5 months old and I'm worried he isnt on track yet. He was born incredibly small, the doctors worried about him my entire pregnancy. He is still currently not up to speed with his weight yet, but hes still having troubles holding up his head. He has yet to roll on his back and onto to his stomach. It mades me upset that he may be not at the same speed as other babies. I am so incredibly thankful that he is here and that I survived (considering i had an incredibly tough labor and delivery). Any wise words of wisdom? Tips? Anything would help. Tia!!!!