I just replaced a 2 gang box that had two switches and 4 14/2's. I added a new light switch and now have 4-14/2 and 1-12/2 (on 15amp circuit with other 14/2's) jammed in the 3 gang box. Is it ok to have 5 groups of wires forces into back of gang and probably bent up. I had to jam the switches in there and press very hard on them while I screwed them into box. Is this normal?

 

No, it's not "normal" but it may be acceptable. There are limits to how many wires/cables can be in any particular size of box but I'll let the electricians answer that question.

 

Here is how it's wired. Its a plastic, old work 3gang box.

 

Cram and jam are harsh words. A better way to do it is to take each cable's wires and retract them into the box using an "s" snake fold with the wires. Practice makes perfect, but I start by pushing the wires down toward the back, then bend them up and then down again until the switch or receptacle has enough "spring" to slip in the holes. Three gang box, you are ok with the capacity.
OOh, your post hit when mine did. Be careful not to press to hard on the old work box, as it could push through the drywall and make for a day.
Double OOh, the picture just showed up. Which cable is "hot"? From what I can determine the middle top 14-2 is. When making a drawing like this, leave out the grounding wires, as they are understood. Makes it clearer.

 

Thanks for the help. I'll see if I can do a more elegant job of bending the wires into an s shape later today. Not to sure if its possible though with them all wired together.

 

I fold my wires parallel to the back of the box and then just a short length out to the device. A 3 gang box should have plenty of room. You are using roughly 30 cubic inches out of approximately 55 cubic inches in the box using box fill calculations.