Whilst you don't need much except a tolerance of midgies to deal with most British holidays, travelling abroad can require the right vaccinations for more countries that you'd think.

Vaccines in pregnancy
As with so many medicines and treatments during pregnancy, women are advised to discuss taking anything with their GP first.
Often this is because medical companies would prefer to err on the side of caution rather than because there is medical proof that something is dangerous to the unborn child and the mother. However, 'live' vaccinations are more of a risk because you are putting some of the disease through your system and if you know you are going to be travelling in the coming year or two, it is advisable to get your vaccines up to date before you try for a baby.
Doctors will help you weigh up the risk of the disease versus the risk of the vaccine in order to make the best possible decision, if you really cannot avoid travelling to a high-risk territory whilst pregnant.
Always make sure the person giving the vaccines knows you are pregnant.

Vaccines when you are still breastfeeding
Again, some manufacturers might err on the side of caution but many vaccines are safe when you are breastfeeding. Make sure you tell the person giving the jabs that you are breastfeeding, to be sure.
Note that you will not be able to pass on the immunity through your milk, to your baby.

Plan ahead
Many vaccinations for travelling abroad need to be spread out or need a few weeks to recover from/take effect.
There is some wonderful country-by-country information on www.traveldoctor.co.uk which tells you about adult and child dosages, how long a jab protects you for, etc.
If you want to find out what you can get via the NHS and what you are likely to have to pay for (even if you have them done at your own surgery), check out the NHS Direct website.