I went through this as well when I first started in June. Kangertech Evod dual coil with a vv batery. I started with 24mg darker colored tobacco flavored juice. I was hitting the hell out of that thing trying to make it all work cause I was sick of smoking after 40 years. What I noticed was about after 3 days of use the coil was done! No rinsing, soaking or anything else was going to bring it back to any useable state. I would get hard choking hits, no vapor, and just a ....ty taste to the point where I was about ready to give it up.
What I found out was, I was an uneducated vaporer! The smokeshop people really didn't give me much info. Not near what you will find on here!
My advice, If your having problems with any of the things I mentioned just put a new coil in it. Life will be good again!
I have since ventured out and tried different flavors, what I've noticed is using lighter colored juices is much more friendlier on coils. I'm down to 6mg nic since June and use a clear flavored juice and coils last about 5 days before performance drops off. I find that I can rinse them out and get another day or so of use, everyones different.
I've rebuilt some coils with mixed levels of success. Main thing keep coils on hand, and buy you a backup battery! A dead battery gave me as much grief or more than a spent coil! Good luck and hang in there! You can beat the cigs with this!