Well, it seems that you are not sure about your current prescription degree. So, it would not be wise for you to get a pair of contact lenses if you are not sure, because that would do harm to your eyes. So, it depends on your specific situation, sometimes if you eyes are as healthy as last time, you are ok. But I still recommend that you try to take an eye exam before you get yourself a pair of new contact lenses.
No, it is not ok for you to wear the contact lenses with an expired prescription. You should have the eye test before you decide to change the new contact lenses. You may have the new prescription now. Thus, you'd better have the eye test again. With the right vision aids, you will feel comfortable at the eyes and see clearly at the things.