G.
Hi J., I had the same issues with my son. I would put him on his tummy and then he would get so frustrated. You are doing the right thing putting toys in front of him etc. I also got just a basic play mat and would start my son on his back and then we would roll to get more tummy time in. If you have a boppy you could try propping him up on his tummy on that so that he can get a better chance to lift his head. My friend suggested it and it seemed to work but just in short intervals.
Don't give up is my advice to you. He will get used to being on his stomach and before you know it he will be rolling back and forth. Hang in there. This time goes so quickly he will be walking before you know it! Good Luck!