If it is NOT a physical irregularity/ailment/physically challenged, then, check out all the following:
1. You are likely, Doing Too Much Too Soon. You’ll need to clarify, what your appropriate fitness goals are. Then, need to design a good Training Program (by yourself, if you know what you are doing…if not, approach a Qualified Professional). This will need to be validated Periodically and Updated as / when Required. Then, stick with the program.
2. You are likely doing them (Exercises) Wrong. Do the Exercises, using proper form. Again, these Exercises and their Intensity need to be part of the Training Program discussed above. If you are not sure how to correctly do your Exercise/s with proper form, approach a Qualified Instructor to teach you that.
3. You are likely Not Eating Properly/Adequately. You will need to Eat Properly and Adequately, to fuel Fitness/Strength Gains. Ensure that you eat a good amount of Healthy Carbohydrates, a good amount of Good Quality Protein with Each Meal, and include Good Fats in your Diet.
4. You are Not Resting (Recovering) Enough. If you are not getting enough Rest every day (a minimum of 8 hours of sleep every day, is a MUST), your Body Cannot Recover Adequately from Workouts.
5. You are Not Keeping yourself Hydrated Enough. Please drink frequently, especially, if you are working out…especially, if you live in a very hot climate.
6. One more thing you might want to consider is again, kind of related to #1 above. You are NOT FIT at this time and are not able to Tolerate the Exercise you are doing now. Either too weak, too much body weight… maybe both.
So, please look at ALL the above factors. Any/All of them could be the cause. You’ll need to identify which ones you’ll need to improve. After taking appropriate corrective steps, the pain you are experiencing will stop.
Hope this helps!