Strong blood flow when meditating
According to my teacher, increased salivation is a good sign. This means your mindfulness of body and of feelings is recovering.

Increased sensation of blood flow is alright as long as it does not cause a headache. A headache would mean you are trying too hard and fighting with yourself. If that were the case then you would want to either chill down a little or take a break.

Breathing speed up soon after sitting means you're no longer blocking it. Allow yourself to make a lot of noise, don't try to be quiet or calm down too soon. Let your breathing by very noisy until it calms down by itself.

Overall it sounds like you are making good progress, just keep going, don't fight yourself and go with your intuition. If I were you I would not stop the retreat now. Just don't generate expectation to get some external insight. The insight is the elephant in the room you can access through being aware of all experiences, esp. ones that you habitually push outside your attention.

While abdomen is the anchor that keeps you from flying away, it does not mean you should block other inner experiences.