CBN dosage - possible tolerance

Hi guys. I was struggling to sleep from May and i was using Hydroxyzine as a sleep aid. I dont like hydroxizine very much because frequently the next day i have drowsiness. I decided to replace hydroxyzine with CBN. I visited a local CBD store and the seller told me that is better to use a tincture with CBD and CBN. I chose a CBD - CBN tincture (full spectrum) with 5% CBD, 5%CBN and 0,2% THC. I started with a dosage of 7mg CBN (and CBT too). He worked well for 10 days but the last night i woke up at about 4am and i did not sleep again. Is it possible to develope tolerance in a such little time or my dosage is low? I was waking up other nights too but i was returning to sleep within 5 minutes. I think to increase my dosage to 10mg CBN for most effective results. Please share your thoughts, i m new in CBD and i dont have experience.