Internet not working properly last couple of days.

The internet has worked fine since I got it till as of two or three days ago.  I am a streamer and can no longer stream because I am not putting out a consistant bitrate anymore.   Could I get my line tested or something to make sure everything is ok or what steps should I take to trouble shooting this problem?  I am plugged directly into the modem with a wire and use no router.  I've tried rebooting the modem/computer etc and can't seem to find a fix for this problem.  Any help wouldbe appreciated please let me know if you need more information.