Macbook Pro hot after installing SSD

About 6 weeks ago I upgraded my 13" Early 2011 Macbook Pro RAM to 8GB and installed a new 500GB Samsung SSD with a clean install of Yosemite, mostly because my old HDD wasn't coping well since upgrading to Mavericks. Overall everything is working fine, and its a lot faster than it was before, except rather annoyingly my Macbook Pro is now getting ridiculously hot on and off for no apparent reason, even when its not really doing anything. I'm sitting here now running nothing but Firefox (no Flash or streaming or anything memory hungry operating), Kindle and Reminders, and its already running at 81 degrees C. Sometimes its going well over the 90 degree mark, with the fans running constantly which is noisy and annoying, plus I usually sit with my laptop on my lap, and its too hot to even put it on my knee. I know its probably not ideal to sit with a laptop on my knee, but I've done it for years and its never been a problem until the SSD upgrade. Activity Monitor shows nothing running that's using much CPU (firefox at 10% is the highest). I'm really annoyed as I though upgrading to a SSD would make things cooler and quieter not hotter and noisier. I've tried googling but can't get any solutions other than that Spotlight might be indexing (it isn't) or something is running in the background (nope). The fans were cleaned when I did the install so they aren't choked up with fluff either. Any ideas what might be causing this?