Welcome to ECF!
To be completely honest, Nicotine has little to no discernable taste. What you could be experiencing is the throat kick from your juice that is attributed from a higher ratio of Propylene Glycol (PG) in your specific flavor. One of the telltale signs you're taking in too much nicotine is the nausea that comes from chain vaping. Perhaps dehydration? In any case, unless your past juice was 24mg/ml or higher; you shouldn't be having any runoff nic side effects from your last juice.
Depending on your setup, you may be looking at a few things:
- Clearomizer / Cartomizer - The liquid inside your wicking material still has the old juice in it. Wash/clean the coil if you can't replace it immediately. Run the new juice through it after letting it sit for a few minutes.
- Rebuildable Tank/Dripping Atomizer - On the off chance you're on a rebuildable setup, just clean out the chamber, replace the wick and coil.
Keep in mind some people are a little intolerant to PG. Some previously decade long chain smokers report vaping is "too rough" because of acid reflux, or even slight food allergies. I'd advise just experimenting with juice samples, look for juice that's higher in VG, and make sure everything is nic free.
Hope this helps!