Hello and welcome to TAS

Is it female pigs showing the problem ? Are they running with uncastrated boars ? It might be that they're having season's and the boars are 'having a go' which might be giving them a bit of pain and stiffness

BUT there are 100 and one things it
could be (and without any of us actually seeing the pigs first hand it's all but speculation

) - so best to think about the following...
Are they off their food ?
Do they have a temperature ?
Have they
definately been drinking ? (I only ask this as I've recently lost weaners due to salt poisoning from lack of water - they start off staggery and progress to wandering around looking disorientated)
Have they recently moved paddock ? Could have sprained or pulled a muscle in over enthusiasm while exploring.
How many pigs do you have and are they all together ? You say two are showing signs - are there others who are okay ? I'm trying to gauge if maybe it's something environmental (problem in the paddock for instance) or if it's illness that is spreading.
Come back to us with an update

Karen x