Thanks for the extra information lynney.
Although you had a relatively straightforward investigative surgery, you should be up and about and not suffering any side-effects. You've not taken any painkillers which is interesting to note as some of them can contribute to the symptoms that you're describing. So we can fairly comfortably rule them out.
I'm presuming that you're eating and drinking relatively well, and (as unpleasant as it may be to enquire) going to the loo with no problems, with no unusual discharge.
Have you been suffering from any abdominal pain or cramps?
I'm presuming you're not asthmatic or diabetic as well.
Are you on any medication regularly (or not) that you were on prior to going in hospital? It is possible that any medication you were taking prior to surgery is now unsuitable for you. However, this is not very common.
It's difficult to give you a definate diagnosis via the web as there are a few options/possibilities to explore etc, which are best done in person by someone who knows you, i.e. GP. If you're symptoms are not easing and you're eating/drinking and mobilising relatively well, then see your GP. They will be aware of the surgery (and findings) so will be able to give you more information and pertinent examination.
I'm sorry I can't be more helpful at this stage, and whilst we could go back and forth for days trying to get down to the route of this, I'd hate for you to delay seeing your GP.
I hope you feel better very soon.