fainting etc

[lsharp]

hi..im 31 weeks pregnant. i have always had problems with fainting dizziness, heart beating very fast etc i have stayed in hospital over night and they cannot find anything wrong. i have seen a neoroligist and they also couldnt find anything wrong. i have been anaemic throughout my pregnancy and my iron levels are now at 9.9 which the hospital said is fine. i cannot understand why this keeps happening because it was happening way before my pregnancy and now is getting worse day by day. i eat a heathy diet with vitamin iron etc can any1 help???