Generally these skin irritations around the mouth and under the chin are related to saliva, drool, pacifier use and food in contact with the skin.
My strategy is to keep the skin clean and dry as much as possible, reduce pacifier time (if using one) and using a barrier cream/moisturizer such as aquaphor.
When there is redness/inflammation/itchiness sometimes a pediatrician may try a small amount of 0.5% hydrocortisone cream once or twice a day for a few days - being careful not to get it too close to the mouth or eyes.
My first question would be to know how your baby is gaining weight. If she is gaining at least a 1/2 ounce per day then it sounds like you are in good shape.
Many babies, as they become more efficient, will be able to fill up in a 10 minute period - especially if you have a good milk supply and a fast flow.
At 3 weeks and 6 weeks, babies have days of cluster feeding in which they feed more frequently (often on the hour). The end result is that your body responds by increasing its supply. The more often a baby eats, the more milk your body has for the baby. This is a good thing.
The every hour feeding is actually a very normal thing at this age and feeding on demand is definitely the preferred method of nursing your baby.
The good news is that over the next couple of months your baby will likely be able to take more at a time and go longer stretches.
Hang in there for now. It sounds like you are doing an amazing job!
Reading your description makes me think of Developmental Hip Dysplasia. Here is a link that has some more info.
DHD is when the hip socket does not completely form. When the peds checks a baby's hips, he/she is looking to see if there is too much movement of the hip joint or if the skin folds are uneven.
Ultrasound would probably be my study of choice in a 2 month old because there is no radiation and the radiologist can watch movement of the hip with the ultrasound. Xrays, in my experience, are more helpful after the 6 month mark.
I would definitely advocate that you see a pediatric orthopedist if DHD is at all a consideration. Early intervention can really make a difference. If caught early, most infants are placed in a harness and that promotes proper development of the hip.
Grace is correct in the usual workup for hydronephrosis. Typically an ultrasound will be done and if hydronephrosis is confirmed a test called a VCUG is done next. A daily dose of antibiotic may be given to prevent bladder/kidney infections if reflux is suspected.
In my experience, many babies with hydronephrosis on prenatal ultrasound have turned out to have very normal kidneys once the workup is done after birth.
Most babies will get their first teeth between 6-9 months. Some will get them sooner and some not until 15 months.
Some babies will be fussier, pull on their ears, drool or have their hands in their mouth more. Some will have gum swelling or purple gums. Other kids will just wake up one morning with a tooth starting to poke through.
Usually diarrhea will present as some combination of looser and more frequent stools. If he seems to be getting dehydrated, you see blood or mucus in the stools, then you should definitely call your pediatrician.