How to tell if baby is hot or cold!

My daughter is a week old now and her first week we noticed when we would pick her up she would feel damp sometimes. I'm assuming that was her sweating now. She's also been getting really fussy at night and not sleeping as much. Today she's starting to have trouble sleeping during the day now. Her back and neck feel really warm and she doesn't have a fever. I've got her down to just a diaper and her back is still warm (we live in MI so it's cold out). I can't tell if/when she's too warm or cold and of course google has me scared since overheating can put them at higher risk for SIDS. Please help put my mind at ease.