Lump under armpit still there after 10 months.

[melcul]

Hi,
I’m male 29yo.
10 months ago (august 2019) i‘ve shaved my armpits with wax, Which left me with some serious skin irritation for at least 3,4 months( redness, pain, inflammation, etc). After about 3 months(october 2019), while i still had inflammation, i also noticed a pea sized lump under my right armpit. At that time i had many painful red bumps and i just thought it was one of them.
I thought it might be due to waxing and i just stopped using deodorants and kept the area clean. It got A bit smaller in size but again in January, I realized it turned red and swollen again (i'm not sure if this was the cause, but i remember using a deodorant 2,3 times again), with no pain, you could easily see something was there, like a peanut when raising my arm. no pain.
The doctor initially thought it was Hidradenitis suppurativa, and i used some antibiotic ointment on it.
Didn’t seem to do much though. Now, after 10 months, the swelling is down, it’s not red anymore, and you can’t see the bump like I would previously do, but if i press on that spot, i can still feel a pea size lump, around half a centimetre in size.
I had it checked again by an advanced nurse practitioner, not a doctor unfortunately, which told me that it may be something like ingrown hair, blocked sweat gland,etc
Should i ask specifically for a soft tissue ultrasound ?
It doesn't seem wise to me to just leave with a lump without knowing what it is.
Anybody with this problem around here ?