When can I touch my toes/Is it my butt?

Hello,

I've been doing stretching exercises for a few weeks now so I can touch my toes with a straight back. So, to become more flexible. After the stretches, I feel a bit better than before, and I can reach further down to my feet.

However, the next day I am just as stiff as I was at the beginning and I can't calm down at all.

Someone also wrote to me here that the cause is most likely the buttocks being too weak. Because the body tries to stand up straight, and then the backs of the legs/hamstrings are strained because the buttocks can't do it.

When I want to do kicks (kickboxing), I can't even lift my leg high enough. I think it's my glute muscle. I really don't know what to do anymore; I just want to become more mobile and flexible.

Do you have any tips or advice?