"I am very sick."
Translation:Je suis très malade.
Malade never uses the verb avoir!!! In French, adjectives could either make use of être or avoir in expressing them in sentences. Same way these two 'notorious' verbs, when using them to form the passé composé, are specific to certain past participles. Unfortunately, you just have to learn them by heart, just the same way you have learnt that the adjective froid uses avoir. But malade on the other hand, always uses être. Examples: J'ai très froid(e) = I'm very cold, Je suis très malade = I'm very sick, J'ai trente huit ans = I'm 38years (old), Je suis entré(e) = I entered, J'ai visité(e) = I visited, etc.. As I said, you have to learn which auxillary verb to use per time by heart. I have come to realise that the more you practise, the more you tend to retain them, and which of the two to use will come to you naturally.