The soreness isn't totally avoidable, but you should be able to reduce it by decreasing your exercise volume and intensity for the first few weeks.
Think of training to get back into the swing of things instead of training hard for the first week or two. Maybe consider doing only two or three moderate sets per muscle group.
If you're planning on being in the iron game for a long time taking two weeks to adjust is nothing. There'll be plenty of time to get huge later.
Fish oils will help with DOMS, but they'll take a while (about a couple weeks to be incorporated into membranes) to have an effect.
By the way, the first workout back after six months and you train arms? WTF?