A month is too long a time to retain whatever was studied. Even the brightest people can technically remember upto 7 days, unless they revise what they are studying. My advice to you would be:
1. Study in batches of 40-45 mins. The brain cannot retain anything read after this time period.
2. Do not drink tea, coffee or cold drinks while studying. These drinks, although, make us feel energetic, they decrease our retention power considerably.
3. Whatever you read in the whole day, give it a quick revision that night before sleeping and once after waking up in the morning.
4. Try and keep one day of the week such that you revise what you have studied the other 6 days on that one day. That will help you retain more.
5. Try to make concepts, stories and brain maps of whatever you study. Elaborate learning is always retained longer.
Revision is the key to remembering anything long term. When you revise something repeatedly, it gets consolidated in your brain. Otherwise it is virtually impossible to recall anything you have read once, as your brain keeps creating new memory paths and removing old ones to make space. The other thing you can do is not to mug up everything you read- that only results in short term memory. Try to understand what you're studying; that is retained better. Use tricks like mnemonics, acronyms and pictorial representation to improve how you remember things. Whatever is taught in the day has to be reread the very same day, and at least looked over in the next one or two days.
It's a common problem seen in students across all the streams. But there is no alternative to revision.
What I will suggest you is to first get your notes organized neatly into different topics.
Mnemonics are very useful while revising. But use a memorable easy to remember phrase while doing so.
Bigger chunks of information can be memorized by putting the information in rhyming words.
Photographic memory can be used to combine images with text to reinforce what you've learned.
Search for 'method of loci' on the net and understand the concept. It's a very effective method to memorize fine details in an answer.
Wish you all the best...