Is my manager scheduling me on less productive days on purpose?

Hey! I have a quick question. I started a new serving job about 4 months ago. I have loved working there for the most part & I havent had any problems except for with three of the five managers. The GM (male) has no scheduled me a fri/sat night in the past three weeks. I just received next weeks schedule, and I was scheduled a Saturday night. AWESOME. So this morning I wake up & the GM changed my Saturday night to a morning shift!! This is the 4th week with no fri/sat night shift. I spoke to the server manager to ask if there was anything I did for the schedule to not be including me. He said it was a mistake & things would get changed. Things just got worse....The GM never speaks to me, he gets upset when I ask him for help & just sighs, & he also sounded completely indifferent to my desperate request to pick up a shift that was left for me, but he gave away to someone else. The other two managers are female. They just seem to dislike me all around. Always sounding annoyed when I call work ( during the right times ) & they seem to just be bothered by me. Am I being discriminated againist? Im 22, mixed race, & I have ethnic natural hair. I just feel helpless. Please anything would help. Thankyou so much