...strength have suffered a greaty? my kicks are high and fast but I've lost a lot of physical strength in my legs and cannot kick hard without hurting my inner thighs
You have been stretching improperly. What you actually did was weakened the muscles which gave you the impression that it was stretched.
It is not the amount of stretching, but the proper type and method of stretching that you should had focused on. You need to give the leg muscles a few days of rest. Stop kicking and stretching for a few days. Using the downtime, read up on proper stretching techniques and startout slow and easy.
If you continue to do the stretches wrong, you will cause permanent damage to the ligaments and tendons. The only way to repair them is with surgery.
What possum says. There is a balance between strength and flexibility which has to be earned over time. You gave up strength for flexibility. Do some strength training but continue to stretch too to maintain (rather than gain more) your flexibility.
Strength training and flexibility training should be trained together.
That's typical when you don't engage in a complete and well-rounded stretching regimen.
I think what you need to do is add in isometric exercises: this adds strength at the range of motion you perform the exercise.
You mention pain in inner thighs... you can reduce some of that pain by performing static stretches at the end of the workout. Normally, soreness after workouts is due to buildup of lactic acid. Simple static stretches just squeeze it out of the muscles.
But inner thigh pain can also be due to tearing of the muscles. In this case, you are kicking uncontrollably too high. That is a result of you being flexible - but not strong enough to control the kick to prevent going "out of bounds". This is called ballistic stretching, and at all costs this should be avoided. So for awhile, don't try to kick as high or as fast; you want to reign in your technique. In the meantime, work on your isometrics for a few weeks until you get comfortable with speed and control.
If you find that as a result of isometrics, you are losing speed and power, then, gradually add in plyometric exercises.
When you do this, do them all on the same workout and give at least 1 day of rest.
And by all means - do you dynamic stretches in the morning (every morning) within 15 minutes of waking; and do them again in your workout immediately after a warmup.