Thanks a lot for your answers! I just went to the roof and saw that my neighbourhood has 5 other networks (which I never knew existed). That explains it partially.
But what is incredible is that, I tried reversely connecting my laptop's WiFi antennae's coax cables to the WiFi adapter. AUX where it's supposed to be Main and Main where it's supposed to be AUX. And voila! The signal strength increased by a bar and the speed by 4-5 times! Now I get 12 MBps (96 mbps) next to the router, which is the maximum speed of the Ethernet, itself, and 4-5 MBps (32-40 mbps) at my worktable!
Thanks everyone, for taking the time out to help.