I've studied French and English at the same time. For a while, expecially after starting French, I mixed them up terribly, but quite soon it wasn't a problem anymore. When I later started Japanese, I had not such a problem: my brain is now used to separating different foreign languages automatically. So if you have a problem now, don't worry, it will solve itself very soon.
As for the other problem: don't use bilingual dictionaries unless you must. You have very good dictionaries online such as https://en.oxforddictionaries.com/ or https://dictionary.cambridge.org/en : always use the monolingual dictionary, know the meaning of the words explained in English, read the examples to consolidate the word in your memory. If you can't make sense of the definition, and only then, check the bilingual dictionary.
I hope it's useful.
Last year, I started to learn Japanese. Since I wasn't persistent, I decided to learn Cantonese instead. The reason I chose it over Japanese because I'm already capable of reading and writing Chinese characters. My goal is to understand Cantonese and speak the language.
I'm also improving my English and Chinese. I might say both languages are at an intermediate level. That's why it's possible for me to learn two or more languages at the same time.
You should emerge in the target language. You could read as many books as you can and listen to a podcast every single day. You could also read the notebook entries posted by members here, read the corrected entries which you could learn from, pay attention to the answers of questions asked or you could ask questions yourself.
In a word, if there's a will, there's a way. Be persistent and don't be afraid of failure.
Hope it helps,