It is completely normal. The more muscular you get, the less flexible and mobile you become. That's why MMA fighters, martial artists etc keep their body weight in the 180s.
The only thing you can do to increase flexibility is to stretch. Try doing yoga on your off days. It's AWESOME for increasing flexibility and mobility.
There are 3 pillars to muscular strength - strength, endurance and flexibility. Most weight lifters have tons of strength and endurance but neglect flexibility.