If you're in pain, the last thing you should do is exercise. If you're tired, fatigued and hurting from a previous workout, listen to your body and REST. you will NOT derail any of your efforts at good health or weight loss because you have to take a couple of days off from your routine.
No one should be exercising when they are in pain or fatigued. that increases your risk for further injury. Take a few days off. believe me, you'll have a much more productive workout if your not in pain or tired. the fact is, exercising every day will not speed up your weight loss. Weight loss is a slow steady process that takes time. I know you want to reach your goal by the time of your wedding, but you have to ask yourself this question,"Do you want to limp down the aisle in pain ?" because that's what's going to happen if you keep pushing yourself too hard.
So, don't beat yourself up because you can't exercise today or even tomorrow. Take a couple of days off. Give your body a rest. Let your batteries recharge and then slowly ease back into your routine.
I don't know how many times a week you do Insanity, but the problem may be you're doing too much for your body to handle. When you slowly ease back into your exercise routine, start with a daily walk. There are members who will tell you how they lost 100+ pounds just by walking and watching what they ate.
As my yoga instructor likes to say,"Don't abuse". It really is okay to take days off from your routine especially if you are injured or in pain. No one should be exercising with chronic pain. that's not healthy.