I assume you put a USB adapter in your home made antenna. You are pretty much out of luck since you have no way into any of the electronics. There are amplifiers that you can put between a antenna and the device but these have limited value since they amplify the noise and interference along with the real signal.
Still if you are going to spend money the best bet is to spend the $75 and buy a commercial solution like the ubiquiti airgrid. engenius has slightly cheaper units like the enh200 for $50 but the ubiquiti has a narrow beam and will go farther.
There is no way you can construct a antenna that comes anywhere close to a commercial one.
Still even with commercial antenna some connections are just not possible. You need clear line of site with no obstructions to get good signal. At certain distances the problem becomes the far end, you may put good antenna on your end but the far end can not hear you. Most times to go any real distance you need direction antenna on both ends of the connections.