Thank you for your question. If you are talking about an itchy rash over the tattoo, it may be a hypersensitivity reaction to the pigment of the tattoo.
In some cases, it can be aggravated by exposure to sunlight. However you should still see a doctor for a thorough examination to determine the cause of the rash.
You can consider increasing the strength of the steroid cream you are using (mild to moderate etc) and increasing the number of times you apply your moisturiser per day (from 2 times to 4 times etc). You can also take antihistamines to help with the rash and itch. Most of these can be purchased over the counter but you probably need a prescription for the stronger steroid creams.
All the best!
Related: The Ultimate Guide to Tattoo Removal in Singapore