My period only lasted 4 days started light with.lots.of clots then turned red with slimy clots mixed.with clear mucus i had.backache and cramps.

Not unusual: The uterus is a muscle, so that when you are passing clots it is squeezing them out and cramps are expected. What you are describing is well within normal variation and if you are otherwise feeling well then you are probably ok to wait to see what happens with your next cycle. If you have any doubts it is never wrong to get checked.