Are you flexible? Maybe you can do the full splits, forwards AND backwards, ooooh! Impressive.
Here's a question: Can you stand and raise your leg past hip height?
No? Well then, my friend, you are a great example of why passive flexibility doesn't mean much in real life functionality.
Passive flexibility is what most people see as "flexible." Doing the splits, touching your toes from a standing position, reaching overhead in a laying position, etc, are all examples of passive flexibility. These are great if you are mush, or if you want to look elongated in a photo....while you're resting. The thing is, if you can lay down with your hands overhead, but you can't do that from a standing or squatting position, that shoulder "flexibility" will do you jack shit, other than being able to reach the TV remote a little easier (in which case, get off your lazy ass and go outside to play!!).
Active flexibility (aka, "mobility") is something I prefer much more than passive flexibility. As an ex-competitor in Taekwondo, I was always jealous of the guys on my team who couldn't touch their toes or do the splits (both of which I could do with ease), but could kick your head before you even knew what happened. I always had trouble with getting my leg up there with being able to apply any force. Stretch all you want, you're not going to really improve your kick that much.
I see this from a lot of newbies at our gym, too: They can fully extend their arms while doing crocodile breathing, but can't do a shoulder press or handstand worth jack, let alone a proper wall slide or overhead squat (by the way, if any of these movements are foreign to you, I invite you to come to a class).
The thing is, flexibility without stability is pretty much worthless, if you're talking about being able to move. It's like being a limp noodle. With the help of someone else (or even gravity), you can be in any position, but you can't do it by yourself. Where do you need the stability to establish the mobility? My bet is your core. This doesn't mean doing a thousand situps. In fact, I hate sit ups. Please don't do them. Also, your core doesn't just compromise of your "abs." There's a whole lot more to it (like your spine stabilizers).
Also, your prime movers need to be able to move. Ever watch someone bend over, and their back rounds? Yea, you actually probably do, too (have someone take a picture of you from the side while you pick up your keys off the floor). Do you hinge from your back, or from your hips? If you're hinging from your back, I'm suspecting a sleep butt (look up "glute amnesia"...I know muscles don't have feelings, but it's a good way to understand kind of what's going on).
Now for the tricky part: which prime mover goes with which limb/joint mobility? I've seen people increase their shoulder mobility by increasing their thoracic stability. I've also seen people increase their hip mobility (ex: squat) by increasing their shoulder stability. I've even seen people increase their back flexibility by increasing their hip stability!
How do you know where in your core you lack the stability, or which prime movers you need to get working again? Well, it depends on you. I can't tell you on a blog, sorry. You are not the same as everyone else. You are an individual, and deserve to be treated as such.