If you use a tampon then there is always a risk of TSS and other health problems.
Massaging your clitoris is masturbation, and it has nothing to do with whether you use a tampon or not and has no effect on your risk of TSS - if anything it may be slightly beneficial in that it will increase vaginal fluids which may replace some of those absorbed by the tampon so lessen vaginal damage cause by tampons drying-out your vaginal walls.
During your periods you are going to be more easily aroused, you will also likely notice you can reach orgasm, multiple orgasms, vaginal and g-spot orgasms (if you choose to masturbate using your fingers or objects in your vagina - also perfectly okay and no increased risk as long as your hands and objects are clean) and ejaculation easier during your periods too. Masturbation during your periods can also help lessen menstrual cramps.
Nurse Alex - TSS is estimated to effect 1 in 700 women in their lifetime, and it is NOT NOT NOT due to poor hygiene, implying that is the case is not only ignorant but offencive towards TSS victims (implying they were dirty) and may put others at risk. TSS is always a risk, the longer a tampon is used for the greater the risk but this isn't the only factor in TSS risks.