yes I was really tired too and when I fould out I was pg again it all made sense as we weren't ttc ... so straight onto the elevit for me and I was fine with a wee nap during the weekends with DH around to mind DS.
are you taking a pg supp as you really need folate and other essential vits & mins during pg? If not, you need to get some and I highly recommend what I take, elevit as they are clinically proven to reduce birth defects and they have a high level of folate (800mgs) great iron and calcium etc. Google them for info.
Hope tiredness passes soon!!