Bug bite won’t go away on my 4 month old

Ma

Help . So my 4 month old got a bug bite about a month ago on his forehead . I tried breast milk but it seems to exasperate it . Any help on what I can put on it ? It will get smaller and go away, then it will come back looking red , then get smaller and go away then come back again! It’s driving me nuts and now my MIL brings it up everytime she sees him , but offers no advice . Anyone know how I can help it go away?