There are countless reasons as to why vision can be getting worse. Most commonly it is short sightedness or myopia which can start in the teenage years. Without an examination by at least an optician it is unfortunately impossible to answer this question accurately.
Often our eyes can become dry during the day as we wear contact lenses and the eyes can feel red and sore. Make sure you use contact lens compatible lubricants during the day. Often if the contact lens sticks onto the surface of the eye the eye layer beneath the contact lens (corneal surface) can become deficient of oxygen and this top layer can break down. This can cause a red sore eye by the end of the day. Making sure the eye is lubricated ensures there is a layer of fluid between the contact lens and the eye where oxygen exchange can occur.
It is also important to ensure good contact lens hygiene. Make sure you dont use your contact lenses beyond the period they are designed for and also that you make sure you change your contact lens case regularly. It is also important to ensure you use an optician recommended solution.
If you're doing all the above then it is a good idea to try a new contact lens. Also throw away your lens case and use a new one and perhaps try a new contact lens storage solution as well.
What's important to note is that if there are lots of flashes of light in the vision, or if there is a darker curtain starting to affect the vision, then an eye examination is required usually within a day or two. This is to make sure there is no retinal tear or detachment.
If there are large floaters which are affecting the vision, there is now a safe and novel laser treatment which can break down and vaporise these floaters. I have had good results using this laser on many patients, but an assessment is needed to make sure you are suitable for such laser therapy.