First issue, your A10 is not fast enough to do 1080p@30fps, especially not with the fast preset.
Recommended to either downscale to 540p AND change the preset to veryfast. the best streams for 540@30 are around 1500-2000 bitrate, any less and you'll lose a lot of quality.
OR
Use this build for OBS.
https://obsproject.com/forum/threads/obs-branch-with-amd-vce-support.13996/ This will enable the use of VCE (Video Codec Engine) via your AMD APU and will take the strain off your CPU. you can use 1080@30 with this build but I would recommend raising your bitrate to 3500 instead of the 1800. You can also use 720p@30 if you dont have 3500 upload.
Second issue, you dont have a game or window in your scene. go through the OBS tutorial and learn how to setup a scene to capture. After you do this you will notice that you will lag more IF you keep your resolution to 1080p, this is because your CPU is not encoding actuall footage of video. before, it was just decoding a blank screen.
Third issue, you need to enable Aero. this will be done in two places, first in OBS, make sure that "disable aero" is
NOT checked. and enable an aero theme in Windows. once that is enabled, you should be able to maintain your fps.