Our guinea pig has very dry skin maybe? About 3-4 days ago is when we noticed. Behind her right ear had all scabs and some flakes which we know she's scratching. Along her back (not her grease gland) also has very flaky skin. There are 2 pretty big scab looking things too which she is probably scratching at. She's eating, drinking, popcorning. There's also some scabs and flakes under her fur behind the neck. We put coconut oil on but that made it a lot worst. Not as irritated looking today as it was yesterday. She seems happy! She turned 1 sometime in July
Hi and welcome!
Please see a vet for a diagnosis. it sounds like it could be a fungal infection or mites (there are two different varieties). All three issues need different treatment; we cannot and are legally not allowed to diagnose just from your description or a picture.
Please DO NOT treat on spec - you are more often than not making things worse rather than better because your oil is not helping with any diagnosis and you are allowing things to get worse with using inappopriate products. Please be aware that cheap broad spectrum shop products are also usually not strong enough to cut through an acute outbreak and should be avoided. Some can even be harmful to guinea pigs!
In the end, you have all the extra cost from your DIY care products as well as needing to treat a more advanced problem by the time you see a vet. Unfortunately, vet cost and health care are in the long run your biggest financial factor when keeping any pet.

It would be good if you started saving up on a weekly or monthly basis so you can always afford to see a vet, especially in an emergency or with severe illness.
If you have only had your guinea pigs less than 2 weeks when the problem started, you can reclaim any vet cost from your pet shop as exposure and infection has happened there if you present the sales receipt together with the vet bill and insist on seeing the store manager.
If your piggies are newly bought, you may be dealing with ringworm (tinea), the most agressive and transmittable form of a fungal infection which can affect all mammals including humans and which is sadly not at all uncommon in shop piggies.
Please be careful when handling your guinea pigs and use good hygiene until you see your vet and know what you are dealing with! The time between infection and outbreak is 10-14 days. You always need to treat all guinea pigs in contact with each other when you are dealing with fungal skin infections or skin parasites.