Answer - In terms of proper cursing, no, it is unlikely. Cursing is intensive magic and for a witch to use that much effort against you then you'd have a much clearer idea of who and why. Curses also have a much more tangible effect and your symptoms don't pinpoint a specific result. Although nightmares are a common effect of cursing I would expect them to be recurring with much more frequent regularity.
Having said that, I'm not dismissing your experiences. What I think has happened is that you have got into a negative cycle with your birthdays and each birthday has reinforced the problem until you have become convinced there is something more sinister going on. I'm not necessarily saying all this is psychological, its perfectly conceivable that the worry you are projecting is creating a pressure of its own - a personal demon that feeds on your fears. As a part of you, this has no power over you or at the very least only the power you allow it. Take away the fear and it will wither and fade away.
As to what you can do. Well you need to break the cycle on both a psychological and a practical level. Acknowledge that the pattern need not continue and understand that birthdays in the past have no bearing on birthdays to come. Make practical plans for your next birthday to be very different. Celebrate with different people perhaps or even go away. Make every effort to change the environment and the way you normally celebrate. Make it clear that you are making the changes and breaking the cycle.
I'd also suggest you look into your own history as to why your birthdays have become such an issue. Has something negative happened on a birthday to trigger these issues. Try meditating to look inward but do a bit of digging as well. I'd try asking parents, grandparents and siblings if they remember anything that might help you. If you can pinpoint the reason and tackle the issue the annual symptoms may well disappear on their own. I'd also look at the significance that a birthday has - namely ageing. Examine your feelings toward getting older. Sometimes our fears turned inwards can be a powerful way almost to curse ourselves. If you do have fears that you are suppressing in your conscious it is not surprising that they come into your dreams.
On a magical level it may well be worth a good ritual cleansing to rid you of the negativity that has built up. Salt baths, aura cleansing with crystals (quartz or selenite) and bringing plants into your living environment will all help to reduce the negativity in your atmosphere.