So 2 days ago I got my guinie pig some new hay becouse I saw he was running low [he runs through hay quickly] but he has not eaten the hay and it has been 1 week I'm worried about him I have tried multiple different types of hay and brands and i do not know what's going on with him. I love him alot and I dont want him to be sick btw he is still eating grains and drinking water
Hi!
Please stop feeding grains - they are fattening and unhealthy for guinea pigs, and likely the main reason why he is not eating healthy hay as much as he should. Switch to feeding preferably timothy hay based pellets and only 1 tablespoon per piggy per day. Also do not overfeed on veg. These two food groups should be seen more as daily treats you feed around the hay (which should make over 85% of what your boy is eating in a day) instead of the mainstay of a guinea pig diet. Too much fattening pellets and veg can impact on the health in long term and can really shorten the life span.
My current guinea pigs on a mostly heay based diet live 1-2 years longer and are overall healthier than those I had a decade ago when it is was normal to feed unhealthy dry mix or high calcium pellets (no choice there) and too much veg, especially fattening carrots. Sadly this misconception is still very widespread.

Take the time to carefully read our diet guide and attached links. You will find them very helpful:
Long Term Balanced General And Special Needs Guinea Pig Diets
Always monitor the weight of a piggy that is not eating as it should more closely:
Weight - Monitoring and Management
If in any doubt, please see a vet!
What to check and look out for in new guinea pigs (vet checks, sexing, parasites&illness) (including your customer rights re. vet care over problems in the settling in period)
Please consider getting your little boy a same sex companion. There is nothing like 'I want what you have' reflex to get piggies eating. Guinea pigs are group animals and not wired to live alone. It impacts on their quality of life, mental and physical health if they lack the round the clock life-long companship that they rely on for constant stimulation for a 5-7 year long average healthy life span, while you live your own life with its own time commitments. Your little boys' needs won't go away when you are too busy to spend much time with him while you can leave two piggies to keep each other amused without feeling guilty - and you get to enjoy the fascinating and very nuanced social interaction that makes guinea pigs so unique! It is the best and most loving gift you can ever make any guinea pig!
Arrival in a home from the perspective of pet shop guinea pigs
Companionship
A Comprehensive Guide to Guinea Pig Boars
You can find much more information on diet, health monitoring, making friends with and understanding social behaviours, safe and unsafe enrichments/toys, spotting early signs of illness and learning what is normal and what via this very useful and practical link here:
Getting Started - New Owners' Most Helpful Guides