J.L.
Studies show that all BC can cause clotting and stroke in those who take it. (Read the label and you'll see the warning in fine print on all brands) And if you have a genetic predisposition to clot easily,smoke, have high blood pressure or heart condition, you are at an even higher risk of having complications with BC and should not use it all.
Yes, you can sometimes feel clots...but usually when it is very serious and ususally in the leg area. It can sometimes appear like a bruise. It can be hot, tender to very painful, or abnormally swollen. However, it isn't so easy to detect if you happen to have a clot in other parts of the body where you can not necessarily feel or see them.
While usually there are no apparent signs a clot has formed, the one exception is if a clot is causing a blockage somewhere you may have the same warning signs of impending stroke...which is often when it's too late to get help. Especially if they're (clots) of the deep vein variety or in the lungs (pulminary embolism). This is why death due to clotting is sudden and often by surprise.
All people get clots, but most people's bodies can break them down and the clots naturally resolve themselves. If and when the clots are formed abnormally (due to BC for instance) and don't break down, they can cause a blockage in the veins or lungs for instance, they can restrict oxygen and cause vision issues and other problems. When clots do not break down, they can cause stroke symptoms...and eventually stroke.
The only way to know what is going on is to see a doctor...maybe not the OB, stop the chemical BC, and even have a genetic blood test done to see if you have a predisposition for clotting. If so you are at higher risk for clotting due to medications such as BC. Even if you don't have a clotting disorder, BC can still cause them. It's just more risky for those with clotting disorders.
Google deep vein thrombosis, stroke, and birth control and stroke for more information. It might be time to find an alternative like natural family planning. It's as effective as BC if done right, but there is no side effect risk. Read: Taking Charge of Your Fertility by Toni Weschler on how to do natural bc.
See: http://www.amazon.com/Taking-Charge-Fertility-Anniversary...
Here is info on YAZ and stroke risk:
http://www.onlinelawyersource.com/yaz-birth-control/stroke/
Here is info on BC in general upping risk of heart attack and stroke:
http://abcnews.go.com/Health/story?id=118178&page=1
Info on deep vein thrombosis:
http://en.wikipedia.org/wiki/Deep_vein_thrombosis
http://www.healthcentral.com/heart-disease/c/19/1812/birt...
Info on pulminary embolism (clot that has travelled to lungs)
http://en.wikipedia.org/wiki/Pulmonary_Embolism