Tired days

Was doing some ball exercises on Monday just simple crunches squats and push ups, I thinl I need to focus more on what I do, I woke up yesterday with a sore back and tender muscles where my arm attaches to my body which I'm not too woried about but the back is a problem I am on the look out for a book or
DVD or VCD of ball exercises to make sure I'm doing things right unfortunatley they all seem to come with a ball GRRRRR I can't find the booklet that came with mine I'll have to have a look later, I bought my self a skipping rope today I figure if its raining I can do a bit of skipping insted of walking I think it's a little more intense than walking too so I might add it on to the end of a walk ...... Guess What...... I can still do cross overs hahahahaha I will definatley need to go bra shopping if I am going to keep up this type of exercise