Ziggy now has another lump come up on his rump

. This one is a different sort of lump, more of a swelling than a scab like the other one.
Took him to a different vet this time as I wanted a second opinion on the original lump anyway. I can’t find a good guinea savvy vet in my area so am having to try my luck with different vets. Anyway, this vet said she didn’t know what either lump was, just that the second lump wasn’t an abscess as she put a fine needle in it and no pus came out. She has suggested removing both lumps under GA and having them tested.
I am really worried about him having the surgery (he’s 5yrs). Atm he is quite well in himself, he has a really good appetite and is a good weight. The lumps do not appear to be painful or worrying him at all. I am so worried that after the surgery he might go downhill, he will be on antibiotics and might stop eating and will be worse than he is now. I will feel so guilty if that happened because it will be my fault for putting him through surgery.
I suppose what I’m asking is....is doing nothing ever an option? Just monitoring the lumps for any changes and looking out for any new lumps?
After losing Treacle so recently I suppose I’m paranoid about losing Ziggy too.