PCV booster is done at 15 months generally. Hexaxim* as the name indicates has 6 components DTaP, ipv ,Hib and hepatitis B vaccine. Generally most of the babies by 18 months would have had sufficient hepatitis B doses and do not need at 18 months.  Generally pentaxim( DTaP,ipv,Hib) is given at 18 months or DTP and ipv is given separately at 18 months Please check with your doctor again if you had enough does of hepatitis B or PCV.