You probably have "phantom pains", which is totally normal after returning from a stress fracture. 13 weeks is a decent amount of time to heal a tibial sfx. The golden rule for returning to running is to ease back in, which it sounds like you're doing. When my daughter made her return, the doc said as long as the discomfort doesn't last longer than a few minutes post run and post icing, it should be ok. If the pain lasts longer than that, take another few days off and try again. More than likely you're just feeling the nerves and irritation that surround the old injury.