I think, Your song is 中国五声调式 (12356) , there is no 4 and 7. it is interesting you use guitar 蓝调 feeling to accompany. IMO, 蓝调 has lots of half notes (like b3 and b5 etc beside 4, 7) besides its rhythm. I guess you can't use D口琴吹A把位's 7 in that case. Bravo !