Blocked noses can be due to several factors such as allergy, catarrh, after antibiotic use or eating a lot of dairy based foods.
You don't just need to have a cold to feel all blocked up. An allergy, either to external, airborne irritants (e.g. environmental pollutants, household cleaners, synthetic air fresheners) or to food substances can cause an on-going blocked nose.
Eating a lot of dairy-based foods is, for example, a common factor in the production of excess mucus, which then blocks the nose.
You could try Sinuforce Nasal Spray, as this is traditionally used for clearing a blocked nose.
At the same time, you may benefit from reducing the amount of cow’s milk and dairy produce you have in your diet, as this class of foods can make you more prone to congestion, nasal inflammation, and allergies. It can also be helpful to keep an eye on how many foods containing refined sugar are creeping into your diet, as these can contribute to sticky, clogging mucus too.
You may find it interesting to read this article - http://www.avogel.co.uk/health/immune-system/blog/constant-blocked-nose/