Please do see a vet.
How long have you had Ruby?
Is it the same sow you posted about last month regarding the same issue? (Thread below)
https://www.theguineapigforum.co.uk/threads/pregnant.198870/#post-2732532
Can I ask why you are giving ivermectin? Do you have a vet diagnosed case of mites in your herd and therefore prescribed ivermectin? I not sure where the advice currently stands (one of our pregnancy experts would need to answer), but there used to be some controversy over whether ivermectin is safe in pregnant/potentially pregnant piggies, so a vet should always be consulted in such cases so the clinical need and risks can be considered, and dosages made accordingly (a vet should always be consulted anyway, ivermectin should not be used unless there is a diagnosed need).
If you do not have a diagnosed clinical need and active case, then Ivermectin should not be used preventatively. Low dosed pet shop products will not cure an active case of mites (they are not strong enough), and using it as a routine preventative can cause resistance thereby meaning an actual diagnosed case can be a lot harder to treat with prescribed meds.
I have also moved your thread to the care sections of the forum where it will receive special attention from the experts. The chat sections (where your post was originally made) are not monitored whereas the care sections are by those of us with specific badges in our signatures.