Also, you mentioned that your Duchy has 25/100 ticking up. This is probably de jure shift into France. In short, your de jure kingdom, the Kingdom of Aquitaine, does not exist, and your de facto liege, the King of France, is absorbing you into his de jure kingdom. If he does, people in your area will like him more, he'll be able to press de jure claims there if he loses the land, and it'll be transferred with France in a gavelkind inheritance, among other things. If you want to have your own kingdom, you basically have 75 years to get Aquitaine or it's gone. If the Duchy of Aquitaine still exists and is as big as it starts as, then try to gain independence with them, let them form Aquitaine, and swear fealty to them.
I noticed that in one game, the duchy of aquitane, but I guess the marriage system is too complicated for me to get it in the time allocated. You can't fabricate claims against other vassals of the same liege (or rather press them through war, I tried), so you are stuck trying to marry into a claim. I am still a rookie at that as with most game concepts. I look every five years for a way, in but unless there is just some random opportunity, I just can't seem to plot a way, as a lot of the time, there ARE no claimants to invite. Any advice on that?