Meditation is not easy and it can take many years of practice to achieve tranquility in meditation. Some forms of Buddhism talk of the 'five hindrances' which have to be worked through in order to achieve tranquility, and anger is considered one of them so it's quite normal to experience frustration.
I personally would not consider meditation relaxing, but more a form of brain training which may result in long term peace, but the actually practice itself is often quite a struggle - depending on the type of meditation you are practicing, of course - and I'm personally wary of people practicing meditation without guidance from a qualified teacher, because it is not easy, especially with ocd. If you want to relax on a day to day basis you might be better trying something else, perhaps something more active, as GB suggests. Guided relaxation scripts which are specifically aimed at achieving in the moment, short term relaxation are slightly different from meditation derived from Buddhist practice ( 'mindfulness of the body' is a buddhist derived practice and is not necessarily relaxing) so tend to be easier to deal with.