In the bible does pentecost always fall on a Sunday, or is this just another Christian tradition?

I see in Leviticus 23:5-6, that Pover is always on the 14th day of the month and the 15th day is the Feast of unleavened bread. Then in verses 7&8, the bible says that the first day is a sabbath. I believe that this is the High sabbath that is mentioned in John19:31. We can see that Jesus was crucified on the pover and that the very next day was the high sabbath. Then in Lev.23:10-11, it says to"bring a sheaf of the first-fruits of your harvest unto the priest: And he shall wave the sheaf on the morrow after the sabbath." Then here's where I get confused, In verses 15-16 it talks about counting 50 days and seven sabbaths. This sounds to me like we are to begin counting from the day after the high sabbath, but verse 16 throws me. Is this talking about the high sabbath or the weekly sabbath?