Well, I couldn't walk for about 3 days after my first ever sustanon shot. You will be sore for a day or two. Its perfectly normal. I remember my second shot I decided to do it first thing in the morning and "Shake it off" as the day went on. Could feel myself stiffening up as the day went on. By 5pm I had to dive into the car to get in, as I could hardly sit! But, I find the injections alot easier now and they knock nothing out of me at all.
One other thing, make sure your injection is absolutely perfect (in otherwise, don't let the needle move at all as it travels in a straight line). Moving the needle can cause discomfort later on that day.