I wouldn't recommend a valsalva to try to clear a blockage. It's too easy to damage something and if there's a infection any relief will be momentary.

Since it's been on again/off again for a few weeks it's probably time to get to the doc. Don't be surprised if he prescribes antibiotics. It may have started as routine viral infection, but the persistent ooze and blockages from that may have let it turn into bacterial in your sinuses. BTDT.

You can also try a steam inhaler and mouthbreathing. A steaming hot cup of strong peppermint tea and a dish towel over your head make a reasonable substitute for a commercial product. Peppermint has anti-inflammatory benefits and may ease the sinal cavities.