Despite what people here are saying, it absolutely is possible to learn a language in six months. It takes the Foreign Service Institute 23-24 weeks to teach a person a Category 1 language [e.g. Spanish] to fluency. Also keep in mind that these people don't have the benefit of living in the country that their target language is spoken in.

The reason some people have trouble learning a language quickly is that they think they can achieve this by attending a language class for 1.5 hours every week. This simply isn't enough. If you want to advance at a quicker rate, you need to put in the hours.

Also, I had the same problem as you when I tried speaking with people in my target language. The way to overcome this is to practice forming sentences in your target language, either by speaking, writing, or both. So, every day after studying you can sit down with a notepad and practice forming sentences that you might use in everyday life. Write down greetings, write down questions that you might ask or that might be asked to you, write down answers to these questions, write down what you would say if you were to introduce yourself, talk about your family, talk about your job, talk about your favorite book, etc etc etc. There are countless things you can write about. If you'd rather not write you can practice speaking these sentences, or you can practice both writing and speaking for maximum effect. The point is that you're training yourself to put words together to formulate sentences, and by the time you have to speak again you'll know how to communicate your message because you've already practiced doing this numerous times on your own.

Don't be too hard on yourself. Your problem is that you tried to do something that you haven't had any practice doing. Practice formulating sentences on your own and you'll be well-prepared for your next language exchange.