Human beings are organic in nature, we are made up of organic molecules. There are lots of organic chemical reactions taking place in the body and most times the end products of this reactions are usually accompanied with odors, sweat is an example of such. Sometimes after washing our clothes even when they look neat, we may notice that they still have some obnoxious smell, Most time you may want to mask the smell with body spray or perfume but this is an ill-practice you need to stop, because you may actually be contributing negatively to the situation. 

However, there are some simple tricks you can employ to resolve this issue always.

For shirts that have been worn and washed but still have odor, Mix a solution of two cups baking soda in a washer tub of lukewarm water. Add the shirts and allow them to soak for a while, then wash with a good soap or detergent with sweet fragrance. If you do not have access to baking soda, vinegar is also a nice option.

Take note that since you are always sweating, you may need to repeat this process in order to avoid it happening again.