Since it's only been 4 days, I think it might be a little too soon to increase it to 90mg. You will run the risk of possible side effects you are fortunate not to be experiencing now. It can take time to find the right dosage and going up slowly might be best. Taking them a little closer together and adding a fourth 60mg might be a better choice. Just my opinion, I'm not a doctor. Even with taking Mestinon you will still need to rest. Just listen to your body. Call your neuro and see what he wants you to do. Take care and let us know how you make out.

Hugs,
Pat