Your action should be a problem of bad posture. There is no thrust in kicking, so you should be kicking the instep or foot. Thigh pain is normal, which means that your leg clamping action is done well and has certain effect. In order to improve your movements, you can try the following methods:

You can hold your hand on the shore and feel the water with one foot, that is, how to put your legs away so that your feet can be pushed out flat.

You can also try to keep your feet shoulder-width apart at home. The toes are separated outward by about 120 degrees. Squatting down and standing up like this is the kick of breaststroke. When swimming in the water, there is also an action of forcibly clamping the legs, which can improve the speed by more than 1/5. Hold your legs until your feet can touch them. After the leg clamping is completed, it should be a full stretch of the whole person.

Generally, when you close your feet, your toes are like ballet movements. Toe jump straight, feet in place, that is, you can take your toes back to the position you just squatted down.

At home, you try to squat down and stand up as I say. You can do this when you go to the swimming pool. There is basically no problem. What swimming problems can be exchanged in the future! I hope I can help you.