Well, the same mistakes I would have translating really word by word from portuguese to english, you can get also translating in the other way around. So, I kindly suggest: don't do it. 

Let's go then to your mistakes:

Faz Favor....

Faz favor de não usar o autoclismo desta sanita para dispor fraldas, pensos higenicos, lençóis de papel, goma de mascar, telemóveis antigas, contas não pagadas, lixo postal, a camisola de sua "ex", esperanças, sonhos ou peixes dourados.

Vocabulário: 

Please: POR favor (when you say "FAZ favor" you mean "do a favor" and it is not really polite...)

don't flush: não dê descarga (em/nos)

Nappies: fraudas

Sanitary towel: word by word is "toalha sanitária" but the name in portuguese is "absorvente" 

paper towels: toalha de papel (usually you can find to dry your hands)

gum= if you translate is going to be "goma de mascar" but in portuguese is " bala" and chewing gum is "chicletes" 

old phones: "telemóveis antigos" -  "telemóvel" is masculine and maybe in Portugal you can heard it, but usually you can say "celulares velhos/antigos"

unpaid bills: contas sem pagar

junk mail: in portuguese we don't have this "expression", so usually are "old mails" = correios antigos/velhos or cartas antigas/velhas 

your ex's sweater: sweater is like a jumper, right? So then is not "camisola". Camisola is the nightdress. So, you can say "o suéter do/da seu/sua ex".

The rest is fine...

However, the whole phrase is going to be:

" Por favor, não jogue no vaso sanitário fraudas, absorventes, toalhas de papel, balas, celulares velhos, contas sem pagar, cartas antigas, suéter do (a) ex, esperanças, sonhos ou peixes dourados." 

>> Não jogue no vaso sanitário = don't flush down in this toilet.

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Eu espero ter te ajudado!

Sou Brasileira, portanto falo o Português do Brasil, com sotaque de Minas Gerais (porém, apenas o sotaque é diferente, para escrever é quase o mesmo português em qualquer lugar) .

Estou disponível para te ajudar a melhorar seu Português! 

I hope helped you!

I'm Brazilian, I speak the Brazilian Portuguese, with the "Minas Gerais" accent (however, is just a different accent, to write down is almost the same Portuguese in everywhere) .

I'm available to help you to improve your Portuguese skills!

In bold are things are wrong or it is not what you would like to say... In blue are the things I couldn't understand so well. And in grey are the things I would suggest something different...

I'm not a teacher or so, but I'm trying to help as I can, alright?

So, let's go to your mistakes:

worthy to be finished => I guess you would like to say that it worths for you write every day even it's not that easy.

So, then I would say just "It is not easy, but worth it!", however you can also say, for example: "It is not easy, but is worth to make it" (or produce it, do it, write it).

 avoid burnout => This one I have no clue about the meaning. But this habit to write really often something can help you to improve your writing skills in another language, improve your vocabulary...

I'm tired because of working  => it is not wrong, but i would say " I'm tired because of MY work"

 "... and I don't have any energy to complete my writing, I write a sentence instead." => You've been repeating a lot the word "writing" and some times you can also use some words to make the links between the sentences. Maybe you could say here: "... and I don't have any energy to complete my text, then I write at least a sentence instead.

lose the momentum => there is an expression "waste time" for this meaning. You could say: " It is a little bit tricky, but I don't want to waste my time doing anything since I could be learning at least a bit of English."

Momentum is hard to be developed => I don't understand so much what you would like to say. So, I guess is " Life is short, we have to enjoy and manage better our time to improve ourselves as much as we can". 

In case I stop writing a day, I will stop writing next day. => I guess you would like to say: " In case I would stop to write one/some day, I would stop writing the next day as well."

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I hope I could help you a bit! Keep writing and improving your skills!