I have an Iphone of unknown model and it is getting rather difficult to charge the thing. Is this something fixable or do I need another one?

The charge cable is not sitting in the slot or something, its like playing tetris for the charging icon to show up and then I have to position it just so in order for it to remain charging... It is so annoying. Since I barely use the Effing thing.
I don't know what model it is, I bought it second hand from a brother... Probably my first mistake. God I miss my old Nokia.