What's the disk usage with Opera closed? Did you find which file or folder is taking up all that space? How is the memory usage? If it's too high, maybe the swap file is getting too big. If you have no idea, you can use a software like Scanner, which is free and portable: http://www.steffengerlach.de/freeware/.
On another hand, bear in mind that you should leave a good % of your SSD free for the sake of its lifespan. I'd say no less than 25%.