My Galaxy S4 can barely connect to Wi-Fi. How do I fix this?

I just got my Galaxy about 3 weeks ago. I love it so far, but my only issue with it is that it's horrible with connecting to Wi-Fi. It gets a very weak signal, to the point the Internet will barely work, and the only way to strengthen the signal is to stand at least 2 feet away from the router antenna. I mean, my bedroom is only 10 feet away from my house's router, and even then I can't pick up a good Wi-Fi signal. My router gives out a pretty strong signal, too: you can be standing outside in the backyard with a laptop and still be able to access the Internet. But it's not just my house, I've had the same issue with every Wi-Fi network I've connected to. My desktop computer, my laptop, my game consoles, my old phone, my family's phones/devices, they all have no issues with Wi-Fi. It's only my Galaxy that can't properly connect.

Any ideas how to fix this? It's getting very annoying, needless to say, especially when I'm trying to do something on my phone.