Re: Timely! And check this:Re: Quckie reminder for all...Re:Gums
Myrrh gum is extremely resinous...and you already have your own Echinacea tincture (if I'm remembering correctly).
My first-best discernment/hunch would be to mix a teaspoon of Myrrh gum powder with around 2T of Echinacea tincture, then pour in about a 1/2 - 3/4 cup of boiling water...and mix thoroughly. After it cools some, swish 2-3 tablespoons for 8-10 minutes (or as long as possible) several times daily.
Another option (for before bed), get some of the macerated Echinacea 'sludge' from the bottle of the tincture jar and mix a bit of that with some Myrrh powder, dry the area of the swelling as thoroughly as possible and pack that mixture onto the swelling, allowing it to 'soak in' overnight.
Until you get the Myrrh, just go 'full force' with the Echinacea.
Oil? It takes around 2 weeks to imbue an oil with an herb to be 'therapeutically good' (and needs to be kept at 90+ degrees F for those two weeks). Of course, the oil will be semi-good sooner :) What you're suggesting would be great (methinks), but 'sooner is better' :) With what you already have on hand (and the Myrrh powder) should be able to knock it out.
Blessings,
Uny