In my experience dmt keeps it strength in vg/pg mix if stored in a dark and cool place, cap on.
Did it ever work for you, when the mix was newly mixed? Did you test the dmt before you mixed it with e-juice?
What kind of e-cig gear do you use? Those cbd carts will need a lot of puffs for you to break through.
How much VG and PG in the e-juice? If you have 70%vg, 30pg juice, you will have trouble, the e-juice will get to thick for the coil to wick it.
please povide some more details.
Blessings