I miss 1 birth control pill in week 1 & the next day i took 2 pills, then in week 2 i miss a pill again & took 2 pills, do i need plan b if i had sex?

Probably not: But it cannot hurt to take a morning after pill. There is a very low chance of pregnancy with no missed pills, but with every missed pill the chances go up a little bit. Better safe than sorry.

You might not have 2: But if you want to be extra cautious this would be a good thing to do. Forgetting two pills in a pack in theory makes enough of a drop in efficacy that you might want to have a back up plan. You could also use barrier methods (condoms) for the rest of this cycle as an added safety measure.