Sleepy brings up a good point. I have to do "fragrance-free" detergent, warm water rinse, no softener (not even the dryer sheets). I'm a sensitive kind of guy, to the point that I have to be careful what I bathe with (rubber duckies excluded, but I can't wear the water wings - tic). I can't do most shampoos, and I can't use something like a Ivory soap for more than one shower, and have to change to something different. Even some of the "gentle" stuff leaves a residue on the skin, and can cause issues... I'll go from sweating like crazy to not sweating at all, to doing some sort of weird sweating in odd places at odd times (ie: back of the neck)... Eczema (atopic dermatitis) is a side-effect of the sweating, and can come and go at various times. It'll usually pop-up easier in the folds of skin, or where clothing is tight on the skin. What I eat can influence the dermatitis also, with cow dairy being the main culprit there, and UV exposure has reared its ugly head more than once on this. Even meds can do it to you... It can take a lot of experimentation on your part to track down what the culprit(s) is (are), and it can be very frustrating. Consult your doc next visit, and see if they have any ideas.
"There but for the grace of God, go I."
"... His mercy endureth for ever."