Modded minecraft lagged, lagging again?

I made a modpack and it was quite lagging (i used 32 bit java) so i reinstalled it to 64bit and it was going without a lagging on far, but when i start it now its lagging again, any ideas?

Your computer probably can't handle the mod then. Or it may not be optimized well.

It's definitely your Hard Drive, try to defragment your hard drive or get an SSD. Most of the time the lag is being caused due to Hard Drive.

You can download program like Defraggler or use Window's inbuilt Defragmentation program. Just click on Start and search for Defragment and defragment all your hard drive and partition. That should help you.