HELP! 18 month old non stop tantruming

My 18 month old has non stop tantrums...screams, rolls around on the ground, arches his back. Even when I hold him, he flails and screams. The only thing that calms him sometimes is cocomelon. My husband and I are at our wits end. We also have a 3 year old and even he becomes upset by his younger brother. Sometimes the tantrums are brought on by something, sometimes no reason at all. I’m afraid there is something wrong with his brain. We have his 18 month check up in 2 weeks, but I wanted to see if any other moms have dealt with this.