Ghast Explosion

When I go inside the portal from overworld

Ghast fireball breaks my portal and this happens to my overworld portal after I exit 

Random Overworld Nether Portal Generation

After I repair my portal into 2x3 default style, My second time I enter Nether and exit again, nether portal generates in random place (near my shelter, estimated coordinate 100 ~ 100 away) and makes me confuse and killed  and pushed from high place by hostile mobs I didn't know behind me, so that I did not recovered my armors and weapon tools

At first Im glad that my first nether places me near fortress and then this happens, makes me anger at all.