There are many asanas that you can try to achieve lower back strength and flexibility which also provide good exercise to the knees. I would recommend quite a few different ones. One of my favourites which you will also enjoy is tolangasana (scales). This is an excellent exercise that strengthens not only the lower back, but also the knees and elbows.

To achieve this pose sit down in padmasana (lotus) and slowly lean backwards using your elbows. Slowly, shift your body weight on the back and lift the legs still maintaining the lotus position. Keep your arms below the buttocks and hold for a few seconds. This exercise is also beneficial for ailments including indigestion and other disorders associated with the digestive system providing them with a gentle internal massage.When you achieve this pose your body is balanced as if a set of weighing scales.

I would recommend you join a local class and practise yoga under guidance of a good yoga teacher. The more you practise, the stronger your immune system will become. Pranayama (breathing exercises) especially kapal bhati help strengthen the sinus and respiratory system and this breathing exercise is an overall tonic for good health and beauty. I advise that you attend a reputable yoga class and ask your teacher about pranayama. You could also make the effort to practise yoga cleansing such as the netis. Again, your teacher can show you how to do this. There are also natural health products on the market that can help hay fever sufferers deal with their symptoms.

I also recommend that you practise sitakari, a pranayama exercise to help balance the body and give yourself a natural pick me-up. Sit down in padmasana (lotus) or siddhasana (perfect pose). Touch the tip of your tongue on the palate of your mouth. The centre of the tongue should meet the lips. Suck the air in through your mouth using the “seeee” sound and hold the breath for as long as your stamina allows. Exhale through the nose. Try this exercise daily for 30 days and you will notice a qualitative difference overall to your respiratory system.

Yes, try Adho Mukha Svanasana Downward-facing Dog. Go into your allfours position, hands under shoulders, knees hip-width apart. Keep your tummy tight. Spread your fingers wide, middle finger facing forward. Press your fingers and palms into the floor. Straighten your arms and push your bum up to the sky. Keep your spine straight and long. Keep your knees soft at first and don’t worry if your heels are not on the ground. Let your head and neck hang comfortably, or look at your belly button. Walk the dog to straighten your legs by working your knees gently. Shuffle your feet and see if you can get those heels to the floor. If not, don’t worry! You should still feel a nice stretch in your hamstrings and glutes. Hold for 3-4 deep breaths or as long as you feel comfortable in the position. To come out, drop back to all fours. This is a fun asana to practice as it also builds upper body strength.