What could possibly be wrong with my baby?

It's nearly 12:00 at night and I'll be phoning the health visitors tomorrow. I'm wondering if anyone has any idea what could be wrong?

His symptoms are:

Very agitated and tenses up. Whilst crying and throwing arms and legs about.

Has been ill recently (throwing milk up) Diarrhoea also. Doctor said it's probably a viral infection. He's been better recently and not been sicking up his milk.

He's also 5 months in 2 tweeks, he is teething so so bad right now. It looks like he has blisters on his gums.

He's out of character right now and I'm not sure if it's his teeth or what is the main reason here! He's happy but he's getting very frustrated and nothing is working to settle him,