Ow, ow, ow

Yesterday after my run I forgot to stretch. I usually do it straight away, but we had to get home quickly and once home I forgot all about it. Well this morning I woke up and ow, ow, ow. My Left Sacro-illiac Joint (SIJ) is very sore. Actually my whole left side of my lower back is sore. It got worse throughout the day and hurts to walk, sit, move - just about everything hurts it. Damn!