For starters, definitely see a doctor. If you have cellulitis and there's a developing abscess, no matter the size, it's best to have it cut and drained by a professional and in a sterile environment. You'll get a prescription for antibiotics too. Be sure to take them as prescribed.
My thoughts on meth's involvement.... One of the most well known side effects of meth is vasoconstriction, which is the tightening of the small blood vessels in the extremities and outer skin layers. One of the jobs blood does as it circulated the body is collect toxins and carry them to the kidneys to be excreted. Blood also brings antibodies and white blood cells to fight the "bad bacteria" that manages to get into our bodies.
I am of the opinion that meth use most certainly can raise your risk of getting cellulitis. Think about it.... There's harmful bacteria all around us, on almost every surface, even our skin. A normal immune system is pretty amazing at fighting it off. However, if you are on meth and subsequently are suffering poor circulation, plus other deficiencies in immune function, then you will have a harder time fighting an infection that gets itself into a minor cut or scrape or bug bite.
A few years ago when I was homeless I got a quarter sized staph infection on my leg, near my knee. I went to the ER and had it taken care of. I was a regular meth user at the time and I slept in a dirty tent and hardly ever showered. I'm quite sure all those things played a role in me getting that cellulitis only leg. (The ER called it "staph" even though they didn't culture it to find out). I may never know just how big of a role each of those factory were in isolation, but I'm 100% convinced my meth use was a pretty big factor.