Welcome and thanks for posting your query to HCM.
It appears from your query that you got irritation by applying toothpaste over the pimple area known as Contact irritant dermatitis(CID). Now the very first thing is to thoroughly clean the area with simple luke warm water or with cold water without rubbing the area. Do cold compressions for multiple times a day. Do not apply anything which is oily or greasy or having irritant potential- so no self medications.
You can apply mild potency steroid cream such as hydrocortisone
mixed with antibiotic preparation which will help you out in both pimples and CID. There will be formation of scab/ crust over the area, do not try to touch or pull the areas. If you feel more of burning and irritation then can apply very thin layer of calamine
As you have big pimples or we say it as cystic acne
so it is better to consult a dermatologist
for long term relief. Please in future always discourage yourself from self medication as for face especially.
Hope this information will be helpful.
Dr Sanjay K Kanodia
MD ( Dermatology and STD/ Venereology)