website slow down after downloading some plugins

After i install 37 plugins for my website, my website is so slow to open the web page and it is too slow to work even in the admin area. For my hosting i have unlimited database, traffic, disk space. Could this be virus in the plugin caused my website slow down. What do you think a bout this? You may have experience about this. If i know the reason, i can find away to solve it. Or if you know how, please guide me.