The stretchy feeling that you might get should not feel like intermittent pain that comes and goes. If it does, make a note of the duration that the pain lasts for and at what intervals does it recur. If there is a pattern, these could be early contractions and you must report them to your doctor immediately.
Keeping yourself well-hydrated is extremely important during pregnancy. Remember to sip water before, during and after your exercise routine to ensure that you do not experience dehydration.