Call you doctor, explain the symptoms & your financial situation. Go to Planned Parenthood. Contact your public health services and ask about low cost-or-free pregnancy checks.
OTC pregnancy checks are not always 100%.
At your age, this is not something to mess with. If you are pregnant, you should have already begun prenatal vitamins and care and you must think of the baby. If you are not pregnant, you need to make sure it is only pre-menopause. There are plenty of things that can cause your periods to stop, but the other symptoms are a worry, as well.
You need to see someone now!