yes
yes
Yes, you should continue to take methotrexate unless your doctor advises you to stop.
Yes, sometimes vets do give methotrexate, but it is in combination with other medications, and usually in extreme cases. If you have human methotrexate, do not attempt to dose it to your dog. This should only be done under vet care. Methotrexate is fatal if not given correctly.
Yes, you can. You will actually be more likely to get infections, and get them worse, when on methotrexate. At some point, you will likely need antibiotics.
You can. There is no interaction between these drugs.
Ask your doctor.
vitamin c
Yes. There is no interaction between the two drugs.
Yes, most antihistamines are safe to take with methotrexate. You should still speak to your doctor about your specific case.
Methotrexate is usually yellow.
There has been some speculation that grapefruit can have an effect on methotrexate levels in your body, but there is not any real evidence that it is true. There is not enough of a concern to list it in the medication precautions.