After having hard exercise I usually around bedtime will get cold and then get a fever and break it by sweating very hard while I sleep. I an wondering why this happens.

Are you going to bed very soon after your workout? You may want to try to do your workout a little earlier. You also may be pushing yourself too hard! I often have to work out late due to my schedule, but I try to cool down and do some walking at the end to cool off and lower my heart rate. Then I take a warm shower, not a super hot shower, before going to bed. Make sure you slow down your workouts towards the end so your body can relax and you won't have to deal with the big changes in body temperature! I know night sweats can be such a pain- I used to get them when going off of a medication (withdrawal symptom) and it would always wake me up.