Sounds as you have picked up a some bugs from your fellow sleepers.
Itchy butt - can be threadworms - you can get over the counter medicines from the pharmacist for these.
itchy skin - you may have caught impetigo which is a very contageous fungal infection and needs to be treated by antfungal creams. Do not share any towels or pillows with anyone and do not touch your baby with the parts that are infected.
The itching in between your fingers could be scabies. These are little mites that burrow under the skin and that's what causes the itching. You will need a special lotion to get rid of them. I'm not sure, but you can purchase that from the pharmacist.
As you have a baby and there seems to be a lot of contageous things going on, I would suggest you see the doctor. If you have impetigo, you will only be able to get medication from the doctor for this.
Best wishes
Do not have any sex until this gets sorted out, otherwise you will be passing it on, and then getting it back again.