Assuming you are not itching because of the patches, or any adhesive products you are using over the top to keep them on, there is no problem with wearing more than one patch.
Many women have to do this to achieve a therapeutic level, however they usually have to pay privately for anything above 100mcg, so if you are able to get 150mcg on the NHS you are very fortunate.
Additionally, if you are itching because your skin is dry, then I would think about androgens as well because these encourage production of the skin's natural oils.