Ive seen that problem when you have a bad , non working bulb , check that all bulbs are working correctly , if thats not the problem then you need to have the wireing checked , good luck .
If your bulbs are ok, then your Indicator relay may need to be replaced, Turn your indicator on then crawl under the dash and listen for the "clicking" sound of the relay. It will be small box or cylinder about the size of a matchbox. hidden somewhere near your steering column. Find it and replace it. Very cheap item!