I have a couple of questions:
1) What are the ohms of the coils you're using?
2) What voltage/wattage are you vaping at?
Thicker juices will take longer to wick and darker juices will gunk up your coils faster. I've been using Kanger EVODS and now Kanger Aeroflow tank and the fastest a coil gunks up is 1 week, with clear liquids I can vape them for sometimes 4 to 5 weeks. I only use low resistance coils (1.8 ohms) and will vape at no more than 4 volts on my Provari. Anything higher than that will burn the liquid and I have to dry burn to clean them up.
In the more than 2 years I've been vaping, I've tried many cartos, clearos, etc. I love the Kanger products because they've been most consistent. I call them "fill and vape" without having to fudge around with them.