Freezing Up, Gray Screen

My Macbook Pro is probably around 3 years old. I've had issues with it every since I purchased it freezing and working wonky. I had been in and out of the Apple Store I can't tell you how many times. Finally, a few years ago after it crashing and losing everything on me about 4 or 5 times within 3-6 months, Apple replaced my hard drive. It seems to have been fine ever since, but then last week it randomly froze up on me and restarted to the gray progress bar screen. This is normally where in the past it wouldn't do anything more and I had to completely wipe it all clean. This time though, it actually restarted and pulled everything back up as it was before it froze. I figured it was, because I had been putting off the OS X Yosemite 10.10.5 update, so I immediately updated and it hasn't done it again.

Until just now. I was online, it froze up and within minutes it was restarting with the gray progress screen. The bar loaded and then it restarted and up came my window at the web page where I left off.

Are thee signs of something more happening? I'm over this. I had so many issues for so long after purchasing and now this.... just trying to be preventative to avoid it crashing again.