If you are using a volcano i hope you aren't doing what most people do and fill the chamber.
Remember that unless it's bagseed weed, you don't need to put more than enough to cover the mesh.
I've tried using less and putting the liquid pad on top but it's never quite the same. The vapor isn't as dense and I get less total bags no matter what strain I'm using.
Here is what I did when I was in a similar situation with my Volcano...
As your vape session goes on and on, you will notice when you're starting to get less vapor and the product is depleted. Eventually you begin to notice how many total bags you're getting per session (which can vary depending on quality, etc..). So what I did and still do when I use my Volcano is PURPOSELY STOP the session a little short so that I have a few bags left. I dump the remaining contents into a jar for storage. After so much time, you'll acquire a nice full jar of brown "re-vape" or "popcorn" as some like to call it. Then when I want to just get a mild high, I simply open the jar, re-grind it, and start vaping at a slightly higher temp than when I stopped the fresh stuff.
Example:
-pack a Volcano chamber full with OG Kush
-vape bag 1 at 362 F, vape bag 2 at 365 F, vape bag 3 at 370 F
-Feeling nicely medicated and sensing that I have about 3-4 bags left so I stop my vapor session and dump contents into the "popcorn" or "re-vape" jar.
-5 days later I'm looking to get some things done around the house but don't want to be couch locked...go find the jar
-Grind up your "popcorn" nice and fine and start bag 1 at 372 F, vape bag 2 at 375 F, vape bag 3 at 377 F, vape bag 4 at 379 F.
This method has worked for years now considering the Volcano was my only vape and method of medicating for a long time. I tend to think of it as a 3 tier system...a 3 would be vaping the POPCORN as mentioned above, a 2 would be vaping enough FRESH stuff that I'm feeling good and still have some vapor left for the popcorn jar (this is my usual method), and a 1 would be an all out FRESH vape until there is nothing left session.
Sorry if this is sloppy or if I confused you at all but I hope it helps your situation.