it wasn't worthwhile to have a part-time job from which you can't make much fortune.这句话没有错.from which...＝from a part-time job ...
例句：a paying job from which I took a leave of absence to do a favor for my friend
第二句应该改为：it wasn't worthwhile to have a part-time job,for which offers low pay.
for 说明原因.