12 month old with new rash - possible reaction but to what?

[MrsSnaplegs]

DS is 12 nearly 13 months old (DC2)
BF to 17 wks then FF on aptamil
Weaned from 20 wks on full diet - no previous issues, seems to dislike potatoes but nothing else
Good weight gain from birth - around 96th percentile, slowed to 91st percentile once mobile, walking since 9 months, happy child, sleeps reasonably well, normally wakes maybe once a night for feed - some nights will wake early (9pm ish) and take an hour or so to settle but most nights will go through till between 4-6 am when he resettles straight away with milk

Rash on back appeared 3-4 days ago, started as what appeared to be nappy rash around area covered by nappy, very red but settled within a couple of hours once drapolene applied (our nappy cream of choice).
Rash now appears different in appearance and area. Starts on back at waistband of nappy and spreads up the full extent of his back. Small, red, pin prick type rash, worse around nappy waistband, almost ezcema type in appearance. He does not seem distressed with it but it is getting worse. Nappies yesterday looser than normal, a couple of episodes of small amounts of vomiting last week which I feel are not related as purely at night and appeared to be linked to the cough he has had since November (we have both had this since we had a cold then, both remain nasally very blocked up and cough is linked I think to that - again not unwell with it just a small baby having trouble dealing with lots of nasal mucus)

Only recent change is introduction of Cows Milk in larger quantities, he has previosuly loved having yoghurts, cheese and milk on his cereal (weetabix). We have not changed anything else in his routine. We started to introduce cows milk as felt he was of an age and was eating enough to be able to get off formula.

I have put a photo on my profile although it is not great I'm afraid as the light in the bathroom isn't good - I can do another one if it helps.

Does anyone have any ideas?

I'm thinking it can't be lactose intolerance because he has previously had no issues with formula but could it be CMP reaction?

Any advise appreciated?

Oh and DD 6 has never had any evidence of allergies except one episode of ? ezcema following swimming - I suspect too much chlorine in pool at the time but nothing since.
I am allergic to penicillin and feel better when I eat less wheat products but no known food intolerences.
DH no known allergies
Only other family history is neice on DH side who was CMP intolerant

Bump

hi just had a look at picture, all i can comment is on my experiance if that is any help. My daughter who is 7 was brought up on aptamil then transferred her to cow milk and she had a similar rash cant be certain if it is the same rash as cant see rash clearly enough but she only developed rash after a while, took her to docs and he said she has a higher tolerance of milk but still intolerantn and to limit milk intake so i stopped all dairy for 1 week and introduced milk products one be one to see what she reacted to and for her it was yogurt and cheese, and she is still sick even now if she has more than 1 ice cream a day or something with cream in

hope that makes sense

or it could be a viral rash which is connected to cold that is quite common as well and should if it is viral settle down in a week

Thank you will go to gp next week and ask

Quick update - clearly viral as now full of cold with a temp proves I shouldn't jump to conclusions!