1st answer to your question : Difficulty is changing every 980 blocks(from what i know). So it is adjusted on every 980 blocks depending on the current network hashrate.
2nd answer to your question : 10 days ago, BTC was around 14k level. Now it's on 11k level. Every BTC price drop results into domino effect for all other coins out there. You can expect minexcoin price to be around $20 dollar level so that is normal.