Sarah2828,
Welcome onboard
That's correct, the liquids restrictions don't apply to products purchased after security as they are security cleared. It only applied to liquids, gels etc that you intend on taking through security. Are you transiting through another airport or flying non-stop to your final destination? If you are transiting through another airport for a connecting flight, ensure anything purchased airside is in a clear, sealed bag with your receipt separate to present at the next security check so you don't get them confiscated. You'll find further details over on the Flights Forum on the following topic:
HAND LUGGAGE REGULATIONS & INCREASED SECURITY .. Q&As. Another consideration is who you are flying with. Some airlines only allow one piece of hand luggage per person to a particular size / weight limit, so you may need to put purchased items in hand luggage and make sure you don't exceed the limits. You may not be permitted a separate bag.
Darren