What ratio is your juice ?. 50/50 pg/vg won't give you much clouds. VG which is thicker creates the cloud. so 70/30 or 80/20 .VG/PG
PG is thin like water but provides little in the way of clouds.
6mg is probably a bit to harsh as well so cut that to 3mg. Easiest way to go is buy a shortfill and add 1 nicotine shot. This gives you a 60ml bottle of 3mg liquid. If you can get Nicotine in VG it will keep your higher % VG so more clouds.
What i want you to look at is the info on your mod. There should be a ohm sign ( looks like a horseshoe) tell me what that is saying numerically if it is different to what the coils rating . ie the coil ohm's is 0.15 but gives a reading much higher or lower then the coil could be the issue but it is possible it's a bad connection, could be eliquid got in where your tank screws on so try cleaning it with a bit of loo roll.
Along with your coil ohms there should also be a guide for how much wattage to use, always use the lower recommended the highest recommendage wattage usually burns the cotton in the coil head.
See if any of the above helps and come back, With a bit more info it maybe easier to resolve your issue if none of the ideas work so far.
@Hamza101