I use bac water to dilute HCG making 10,000 iu's up at a time, which I keep refrigerated. I use it up in four weeks. I inject using an insulin syringe. I shoot it into my ab muscle near my navel (within 6"). Never had a problem with burning or stinging. Sometimes, the needle bends though, which is a bitch. I am going to switch away from superfine to fine the next time I buy syringes.
I do sometimes get burning/stinging with the test cyp shots. The needle is a 24 gauge, about an inch long. I inject into my thigh muscle because it is more awkward to reach my glutes. Naturally, there is less if any fat on my thighs, where as there is some on my ass cheeks (no shredded thong butt here, ha, ha).
Does anyone know of any sides from doing 2,500 iu a week of HCG for several months? So far, I haven't noticed anything other than feeling a bit jacked on the days I use it. I have been using this for the last six months.