On rare occasions it happened that I sold a photo immediately after it is loaded (about a week). I think this happens because some buyers are viewing the latest photos that are loaded on the system, and they are attracted to some of them. Normally the photos are searched through keywords and, given the high number of online stock photos available, hardly the first sale occurs before 3 months. Consider that if a picture is sold after three months statistically it has a chance to be sold again four times in a year, and this amount of sales is good for a single photo. Continue to upload photos and sales will come!
your portfolio is very small yet and people have to find you. it took me 3 months before my first sale, and with almost 800 images on line now, I still have only 160 sales... its a number game and we are all a needle in a hay stack here. work on key words and have a unique image and you will be found, but be patient too and add more photos and illustrations!
You only have 13 images in your portfolio. Unless someone is specifically looking for an image of a frame, no sales. Keep shooting and diversify. If you look at other portfolios, some may specializ in a theme like farming, or agriculture, but no one has just images of tractors.