Okay, so if you are experiencing random itchy bites concentrated in areas on or below your knees it's possible it could be one of two things:
1) chiggers. chiggers are commonly found on long tall grasses but it's not unusual to have them in your lawn. Think about it, how often do you come in contact with grass? Do you ever walk across your lawn, walk on the grass if there is no sidewalk, or play with a kid in the grass? If so, there is definitely a chance it's chiggers. If it's chiggers there is good news and bad news. The bad news is that a chigger "bite" is actually the site where a chigger injects/releases a teeny tiny barb into your skin which causes the irritation, and there is really no way of getting it out or stopping the itch (trust me, anti-itch creams and bleach won't do the trick). The good news is that the bites will go away on there own in about 7 days.
2)fleas or mites. if you are finding these bites on you and you have a pet there is a good chance your pet is bringing these pests inside to you. Fleas and mites will stay on any surface, especially carpeting, but need a live host for blood. I would recommend getting your pets rechecked for fleas and mites and then shampooing your carpets or getting a pest bomb.
I hope this helps!