The fever as a sign of pregnancy is not authentic as it can be due to many reasons. Although few ladies complaint about fever as early sign but it is not a confirm sign. The authentic sign is missing period at due dates. If you have missed periods, then test HCG levels in blood and in urine.
What would give you the impression pregnancy can cause fever. A slightly elevated temp has hundreds of possibilities. Number one, it could be a decrease in fluid intake. It may be a sign of a coming cold. It may be due to enviorment temp. Just increase your fluid intake and if it continues to rise, it is time to seek professional advice. I wish you well