eruption cyst

my little boy has had 5 teeth come through now, and think his 6th one is coming through, but noticed his gum looked dark purple this morning and googled it and said it could be this, i rang the doctor just for some advice and they just basically said to give him calpole, he definitely seems less happy than usual and didn’t know if anyone else’s little ones had this and could offer some advise? and how long it usually takes for the tooth to come through and for it to go, thank you x