Yea I have this problem too because I am a short guy like you. So, basically what the others have been saying move the head and keep in moving. Also, start timing his jab, make him miss and use the a jab of your own to come inside and smother him. Another big key that was mentioned already is use different angles use lateral movement to keep youropponent guessing.

This is what I have done when I am fighting somebody that is taller than me and has longer arms than me.(which is pretty frequent lol) Also, watching Ricky Hatton over the years has helped me a lot too.