Aggravation of ongoing hamstring strain

I have been struggling with rehabilitation for a hamstring injury for quite a few months now. The problem initially occurred during a warm up for a game (football). I've been to see a physio quite a few times, and recently I have been given a set of strengthening exercises to do 3 times per week in order to allow me to get back to running and playing sports asap.

I recently aggravated the injury slightly. My question is, should I persist with the strengthening activities anyway? Or is it better to give the hamstring some time to feel less painful/ tight?

Thanks
Euan