Strengthening immune system

Hello,

I am trying to strengthen my immune system and generally live healthier/take care of my self better.
I have been doing lots of research and recently started changing my diet and lifestyle slowly to treat my body better.
Currently i havet started taking - garlic, vitamin c, echinacea and zinc all in one tablet, and spirulina tablets, a cup of green
tea with breakfast, i cut out my ribena mixed with water drink, now i drink water with freshly squozen lemon only as we have lemon and orange trees. I do not drink coffee at all or soft drinks (i never have) and i eat plenty of vegetables every dinner.
I am wondering if there is anything else i can add or change to make me healthier in general?
also how long would it take roughly before my immune system starts to become stronger?
I do gym nearly everyday, and sleep fairly well.

Thanks