If the pictures are large in size it will not let you post. Sometimes i have that issue with my phone pics because the resolution on the phone is set to high quality.
If you go into gallery, edit the pic, crop it and re-save it should let you post more than 1.
At that, you need to upload each 1 manually. So when the pop up comes up you hit "attach" 1 by 1 for each pic, then scroll down that pop up window and hit close, it will go back to your posting page.