Welcome to the group.
I am no expert here, but will offer some thoughts for consideration.
First, search on this site for trimix, bimix, caverject, quadmix, and penile injections. There are many good threads on the topic, including several that mention dosage amounts, side effects and treatments.
Which trimix formula are you using? There are several.
Several here who started with "standard" trimix (30 mg papaverine, 1 mg phentolamine, 10mcg alprostadil (aka PGE-1) were advised to begin with 0.1cc and found that was too much for them. Have seen one guy here who ended up with 0.03cc being his best dosage, another with 0.05cc....so there is nothing magical about the 0.1cc except that it seems to be the most commonly mentioned starting point that is suggested by urologists for standard trimix.
I read a report that indicated that 40+% of men report pain from Caverject, which is alprostadil (PGE-1). The same report mentioned that around 3% of men report pain from trimix, so you might be among that 3%.
Some here....biker90 for one....reported that at the 0.1cc level of trimix, he had priapism and significant aching. He ended up using 0.03cc, but again, that is just his situation.
My compounding pharmacy says the trimix has a maximum shelf life of 90 days, but whether 90 or 60, it is supposedly short.
Did you experience the same pain with 0.1 cc as with 0.15 cc? Have you tried a dose less than 0.1cc to see if the erections are good but with less aching?
Sudafed and Extra Strength Neo-Synephrine spray are used to get rid of prolonged erections, but I am not sure if the erection is causing your aching or the presence of the alprostadil...but am mentioning in any case.
If you continue to experience pain at any level of trimix, you might consider trying quadmix or bimix. Bimix does not contain alprostadil. Quadmix does contain it, but that 4 drug cocktail requires even less drug to be injected than trimix and supposedly has fewer incidences of significant aching.
Sorry to ramble on. Hope this helps a little bit.