I have a small lump on my breast that is very sore. My baby has been sick for a few days and not nursing as often or well as usual. Could that have something to do with it?

It is possible that you have a plugged duct, but any lump that does not get smaller within a week should be examined by a doctor. Often, plugged ducts occur because of inadequate drainage from the breast. This could happen because a woman has an overabundant supply of milk, when the baby doesn't nurse as well as usual for some reason, or something as simple as a missed feeding. Other factors that can lead to a plugged duct: a bra that is too tight (underwire bras appear to be common problems), extreme fatigue, inadequate hydration (plugged ducts are often more common in the dry winter months, possibly because hydration is not maintained as well). To resolve a plugged duct: nurse the affected side first, nurse more frequently (or pump), point the baby's chin toward the plug, moist heat, gentle massage, increase fluid intake.

I have had a sore spot on my breast for two days, and now all of a sudden, I feel like I got hit by a truck. I have a fever and chills, my breast feels hot, and I'm achy. What could it be?

It sounds like you have the symptoms of mastitis. Mastitis sometimes begins with an unresolved plugged duct, but it can also be the result of an infection that enters the breast tissue by way of a nipple fissure, or by simply failing to change wet nursing pads. For resolution of the infection: nurse more frequently beginning on the affected side, get as much rest as possible, acetaminophen or ibuprofen may help with symptoms that are causing discomfort, increase fluid intake so urination is clear, apply moist heat, some moms take extra Vitamin C, garlic, and/or echinacea and find that helps. If your symptoms are not improving within 24 hours, you should consider checking in with your doctor. If you do take antibiotics for mastitis, keep an eye out for the development of yeast overgrowth (candida) in both your nipples and the baby's mouth as a thrush outbreak is often preceded by antibiotic use. Some moms find that they can prevent a yeast overgrowth while taking antibiotics if they eat yogurt with live cultures (acidophilus) or if they take acidophilus in capsule form (found in the refrigerated section of a health food store) several times daily while on the antibiotic.
***Added note: It used to be commonplace advice to wean because of mastitis. Although current research indicates that continued breastfeeding is best (the infection is in the breast tissue--not the milk), sometimes moms are advised to discontinue breastfeeding. This is something to discuss and consider carefully as discontinuing breastfeeding may slow down the healing process and lead to a breast abcess.