Try to increase your RAM.
Or open your Launcher, click Edit Profile, check JVM Arguments. There you will see -Xmx1G . The value '1' represents the RAM alotted for Minecraft. Try using 2-4, depending on your RAM. I have 6GB RAM, so I only put -Xmx2G or -Xmx3G .
Hope this helps
PS: I have a crap PC, don't complain for having 30-40 fps, I commonly get 20-30 fps only -.-
And try stacking it up with Optifine and use a resource pack that can load faster. It will make your fps higher.